The verb internalize means to take an idea, belief, lesson, feeling, or experience into your own mind so that it becomes part of how you think, feel, or behave. Depending on the context, you may want a simpler, more formal, or more precise alternative.
Choosing the right synonym matters because words such as absorb, learn, adopt, accept, embrace, incorporate, and take to heart overlap with internalize but are not always interchangeable. This guide explains the differences and shows how to use each option naturally in academic writing, business communication, emails, everyday conversation, and other settings.
Quick Answer
Useful synonyms for internalize include absorb, learn, understand, adopt, accept, embrace, incorporate, assimilate, take to heart, take in, integrate, embody, and make your own. The best choice depends on whether you mean learning information, accepting a belief, processing an emotion, or making an idea part of your behavior.
Quick List of Synonyms for Internalize
Closest and Most Useful Alternatives
- Absorb
- Take in
- Assimilate
- Incorporate
- Integrate
- Adopt
- Embrace
- Accept
- Learn
- Understand
- Take to heart
- Make your own
- Become accustomed to
- Put into practice
- Apply
- Embed
- Ingrain
- Instill
- Inculcate
- Embody
More Formal Alternatives
- Assimilate
- Incorporate
- Integrate
- Internalize and apply
- Absorb
- Adopt
- Inculcate
- Embed
- Operationalize
- Institutionalize
Casual Alternatives
- Take in
- Get
- Learn
- Take to heart
- Make it your own
- Get used to
- Let it sink in
Formal Alternatives to Internalize
1. Assimilate
Meaning: To take in information or ideas and understand them as part of your existing knowledge.
Explanation: Assimilate is one of the closest formal alternatives to internalize when discussing knowledge, information, or cultural ideas.
Example:
Students gradually assimilated the new concepts into their existing knowledge.
Best Use: Academic writing, education, research, and professional discussions.
Worst Use: Avoid it when you specifically mean accepting an emotional belief.
Tone: Formal and academic.
2. Incorporate
Meaning: To include something as part of a larger system, idea, or practice.
Explanation: Incorporate focuses on making something part of an existing whole. It does not always imply that the idea has become personally accepted.
Example:
The team incorporated the new safety procedures into its daily routine.
Best Use: Business, technical writing, policies, and professional communication.
Worst Use: It may be inaccurate if you mean a deeply personal emotional change.
Tone: Professional and neutral.
3. Integrate
Meaning: To combine something with an existing system, knowledge base, or way of thinking.
Example:
The researcher integrated the new findings into her theoretical framework.
Best Use: Academic, professional, technical, and educational writing.
Worst Use: It may sound too technical for a simple personal conversation.
Tone: Formal and precise.
4. Adopt
Meaning: To begin accepting or using an idea, belief, method, or practice.
Example:
The company adopted a more flexible approach to remote work.
Best Use: Policies, beliefs, methods, strategies, and professional communication.
Worst Use: It does not necessarily mean the idea has become deeply rooted in someone’s thinking.
Tone: Neutral to formal.
5. Embrace
Meaning: To accept something willingly and often enthusiastically.
Example:
She embraced the idea that mistakes could help her improve.
Best Use: Personal development, leadership, motivational writing, and general communication.
Worst Use: Avoid it when you need a completely neutral description of learning.
Tone: Positive and expressive.
6. Absorb
Meaning: To take in and understand information, knowledge, or an experience.
Example:
The trainees quickly absorbed the new information.
Best Use: Education, training, presentations, and everyday writing.
Worst Use: It can sound less precise than internalize when discussing deep personal beliefs.
Tone: Neutral.
7. Embed
Meaning: To establish something firmly within a system, habit, or way of thinking.
Example:
The training was designed to embed good communication habits within the organization.
Best Use: Business, organizational development, policies, and systems.
Worst Use: It can sound overly technical when describing ordinary learning.
Tone: Formal and professional.
8. Inculcate
Meaning: To teach an idea, value, or habit repeatedly until it becomes established.
Example:
The program aims to inculcate strong ethical values in young professionals.
Best Use: Formal writing about education, values, discipline, and social development.
Worst Use: Avoid it in casual conversation because it sounds highly formal.
Tone: Very formal.
9. Assimilate Knowledge
Meaning: To understand and absorb new knowledge so it becomes part of what you already know.
Example:
Students need time to assimilate knowledge before applying it independently.
Best Use: Academic and educational writing.
Worst Use: It is unnecessary when a simpler phrase such as learn is enough.
Tone: Academic.
10. Operationalize
Meaning: To turn an idea or principle into something that can be applied in practice.
Example:
The organization operationalized its new values through updated workplace policies.
Best Use: Business, research, management, and technical contexts.
Worst Use: It is not a direct synonym for personal emotional internalization.
Tone: Highly professional and technical.
Semi-Formal and Neutral Alternatives
1. Learn
Meaning: To gain knowledge or understanding.
Example:
Employees learned the new procedures during training.
Best Use: Education, workplace communication, and everyday writing.
Worst Use: It may be too broad when you specifically mean making an idea part of your beliefs.
Tone: Neutral.
2. Understand
Meaning: To grasp the meaning or importance of something.
Example:
After the discussion, he understood why the policy was necessary.
Best Use: General communication and education.
Worst Use: Understanding something does not necessarily mean internalizing it.
Tone: Neutral.
3. Accept
Meaning: To recognize or agree that something is true, valid, or real.
Example:
She eventually accepted the feedback and began making changes.
Best Use: Beliefs, facts, criticism, and personal situations.
Worst Use: It does not always suggest that the idea has become part of someone’s behavior.
Tone: Neutral.
4. Take to Heart
Meaning: To consider something seriously and allow it to affect your thoughts or actions.
Example:
He took the teacher’s advice to heart.
Best Use: Personal advice, criticism, lessons, and emotional situations.
Worst Use: It is less suitable for technical or formal academic writing.
Tone: Personal and conversational.
5. Take In
Meaning: To receive, notice, understand, or absorb information.
Example:
It took her a few minutes to take in everything she had learned.
Best Use: Everyday speech and informal writing.
Worst Use: It may be too vague in formal documents.
Tone: Casual to neutral.
6. Make Your Own
Meaning: To accept an idea or approach and adapt it as something personally meaningful or useful.
Example:
Over time, he made the team’s leadership principles his own.
Best Use: Personal development and conversational writing.
Worst Use: Avoid it in highly formal academic writing.
Tone: Conversational.
7. Integrate Into
Meaning: To make something part of an existing system, habit, or way of thinking.
Example:
She integrated the feedback into her writing process.
Best Use: Work, education, writing, and personal development.
Worst Use: It may sound too formal for a simple conversation.
Tone: Neutral to professional.
8. Put Into Practice
Meaning: To use something learned or understood in real situations.
Example:
The students put the communication techniques into practice.
Best Use: Training, education, workplace skills, and instructions.
Worst Use: It describes application more than mental acceptance.
Tone: Neutral.
9. Apply
Meaning: To use knowledge, principles, or lessons in a particular situation.
Example:
Employees were encouraged to apply what they learned during the workshop.
Best Use: Professional, academic, and educational contexts.
Worst Use: It does not necessarily mean the knowledge has become an internal belief.
Tone: Neutral and professional.
10. Get Used To
Meaning: To become familiar or comfortable with something over time.
Example:
The new employees gradually got used to the company’s communication style.
Best Use: Everyday conversation.
Worst Use: It is not a good replacement when internalize means accepting a belief or value.
Tone: Casual.
Informal and Casual Alternatives
1. Let It Sink In
Meaning: To give yourself time to fully understand or emotionally process something.
Example:
I needed a little time to let the lesson sink in.
When It Sounds Natural: Conversations about advice, news, lessons, or important experiences.
When to Avoid It: Formal reports and academic papers.
Tone: Casual and natural.
2. Get It
Meaning: To understand something.
Example:
Once she saw the example, she got it.
When It Sounds Natural: Everyday conversation.
When to Avoid It: Professional reports or academic writing.
Tone: Very casual.
3. Take It On Board
Meaning: To listen to advice or criticism and consider it seriously.
Example:
I took the manager’s feedback on board and changed my approach.
When It Sounds Natural: Workplace conversations and informal professional communication.
When to Avoid It: Very formal academic writing.
Tone: Conversational and professional.
4. Make It Part of You
Meaning: To allow an idea, habit, or value to become deeply connected to your behavior or identity.
Example:
With practice, she made the new habits part of her daily routine.
When It Sounds Natural: Personal development and reflective writing.
When to Avoid It: Technical reports.
Tone: Personal and expressive.
5. Get Into the Habit Of
Meaning: To make an action increasingly natural through repetition.
Example:
He got into the habit of reviewing his work before submitting it.
When It Sounds Natural: Habits and behavior.
When to Avoid It: When discussing beliefs or information rather than repeated actions.
Tone: Casual to neutral.
True Synonyms vs. Contextual Alternatives
Not every word listed above can replace internalize in every sentence. The difference usually comes down to what is being internalized and what happens afterward.
| Type | What It Means | Can It Replace the Original? |
|---|---|---|
| True or very close synonym | Taking an idea, lesson, or value into one’s thinking | Often |
| Near synonym | Similar process with a slightly different emphasis | Sometimes |
| Contextual alternative | Works in a particular situation | Depends on context |
| Broader expression | Describes a larger process that may include internalization | Sometimes |
| Narrower expression | Describes one specific aspect of internalization | Only in specific contexts |
For example, absorb works well with information, while take to heart works better with advice or criticism. Adopt focuses on acceptance or use, whereas integrate focuses on making something part of an existing system.
Business Writing
In business writing, internalize often describes learning a principle, understanding a strategy, or making a new process part of normal work.
Useful alternatives include:
- Absorb
- Adopt
- Incorporate
- Integrate
- Apply
- Embed
- Put into practice
Example:
Instead of:
Employees must internalize the company’s new customer-service standards.
You could write:
Employees must adopt the company’s new customer-service standards.
If you mean actual workplace behavior, you could say:
Employees must put the new customer-service standards into practice.
The second version focuses more clearly on action.
Corporate Communication
Corporate documents often benefit from precise wording.
Example
Less precise:
Staff should internalize the company’s new values.
More specific:
Staff should incorporate the company’s new values into their daily decisions.
Here, incorporate makes the expected behavior clearer.
For reports, policies, and announcements, adopt, incorporate, integrate, embed, and apply are often more precise than repeatedly using internalize.
Academic Writing
In academic writing, the best alternative depends on the subject.
For knowledge:
Students assimilate new concepts through repeated practice.
Understanding:
Students develop an understanding of the underlying theory.
For beliefs:
Participants adopt new perspectives after the intervention.
Application:
Students apply the principles learned during the course.
Avoid replacing internalize with understand automatically. Understanding something and making it part of one’s thinking are related but different ideas.
Customer Service
Customer-service writing usually benefits from simple and direct language.
Instead of:
We hope you internalize our recommendations.
Use:
We hope you take our recommendations to heart.
Or:
We encourage you to put these recommendations into practice.
These alternatives sound more natural and customer-friendly.
Legal Writing
Legal writing requires particular care because similar words can have different meanings.
Internalize may describe a psychological or organizational process, but terms such as adopt, incorporate, accept, implement, or comply with can describe different legal or procedural actions.
For example:
The company adopted the revised policy.
does not necessarily mean:
The company internalized the revised policy.
The first statement concerns formal acceptance or implementation. The second suggests a deeper change in thinking or behavior.
For legal documents, choose the term that describes the exact action rather than choosing a synonym simply because it sounds formal.
Email Communication
Professional emails usually sound clearer when you replace internalize with a more specific verb.
Examples include:
- Review the feedback
- Consider the recommendation
- Adopt the new process
- Apply the guidance
- Incorporate the changes
- Put the lessons into practice
- Take the feedback on board
The best choice depends on what you want the recipient to do.
Email Examples
Client Communication
Subject: Follow-Up on Your Feedback
EmailFollow-Up on Your Feedback
Follow-Up on Your Feedback
Thank you for sharing your feedback on the latest proposal.
We have reviewed your comments and incorporated the key suggestions into the revised version. We also adjusted the timeline to reflect the priorities you outlined.
Please let us know if you would like us to make any further changes.
Best,
Alex
Here, incorporated is more precise than internalized because the feedback was directly added to the proposal.
Project Update
Subject: Updated Project Process
EmailUpdated Project Process
Updated Project Process
Hi Team,
Following yesterday’s training session, please apply the new review process to all projects starting Monday.
The updated checklist is attached for reference. If anything is unclear, please raise the question before beginning your next review.
Thanks,
Maya
Apply works because the email concerns using newly learned information in practice.
Academic Communication
Subject: Feedback on Your Assignment
EmailFeedback on Your Assignment
Feedback on Your Assignment
Hi Daniel,
I reviewed your revised assignment and can see that you have taken the earlier feedback on board.
Your argument is clearer, and the supporting examples are now better connected to your main point. Continue using this approach in your next draft.
Best,
Professor Lee
Taken the feedback on board naturally describes serious consideration of advice.
Internal Workplace Email
Subject: New Communication Guidelines
EmailNew Communication Guidelines
New Communication Guidelines
Hi Everyone,
Please review the new communication guidelines before your next client meeting.
The goal is not simply to learn the guidelines but to put them into practice during everyday client interactions. We will discuss any questions during Friday’s team meeting.
Thanks,
Jordan
Put them into practice clearly communicates the expected behavior.
Customer Service
Subject: Following Up on Your Request
EmailFollowing Up on Your Request
Following Up on Your Request
Hello,
Thank you for contacting us and explaining your concerns.
We have taken your comments on board and have updated the information provided on your account. We appreciate you bringing the issue to our attention.
Please contact us again if you need any additional assistance.
Kind regards,
Customer Support Team
Here, taken your comments on board sounds natural and polite.
Short Dialogue Examples
Workplace
Person A: Did you understand the new process?
Person B: Yes. I’ve taken the main points on board, and I’ll start using them today.
Classroom
Person A: Do you think you’ve learned the new concept?
Person B: I understand it better now, but I need more practice before I can really apply it.
Customer Service
Person A: Will you consider our feedback?
Person B: Absolutely. We’ve taken it to heart and will review the issue again.
Casual Conversation
Person A: Did your coach’s advice help?
Person B: Definitely. I let it sink in before deciding what to change.
Professional Discussion
Person A: How will the new principles affect the team?
Person B: We need to integrate them into our normal decision-making process.
How to Replace “Internalize” in a Sentence
Example 1
Original:
Students need to internalize the basic principles.
Alternative:
Students need to absorb the basic principles.
Why it works:
Absorb emphasizes learning and understanding.
Example 2
Original:
Employees should internalize the new safety procedures.
Alternative:
Employees should put the new safety procedures into practice.
Why it works:
The alternative focuses on behavior rather than mental acceptance.
Example 3
Original:
She internalized the criticism.
Alternative:
She took the criticism to heart.
Why it works:
The alternative highlights the personal and emotional impact.
Example 4
Original:
The company wants employees to internalize its values.
Alternative:
The company wants employees to embrace its values.
Why it works:
Embrace suggests willing acceptance and support.
Example 5
Original:
He internalized the new information.
Alternative:
He assimilated the new information.
Why it works:
Assimilate works particularly well when new information becomes part of existing knowledge.
Example 6
Original:
The team internalized the lessons from the project.
Alternative:
The team learned from the project and applied those lessons.
Why it works:
This version makes the learning-and-action process explicit.
Example 7
Original:
She internalized the company’s expectations.
Alternative:
She adopted the company’s expectations as part of her approach to work.
Why it works:
The alternative explains what accepting the expectations means in practice.
Example 8
Original:
The students internalized the teacher’s advice.
Alternative:
The students took the teacher’s advice to heart.
Why it works:
This sounds natural when the advice has a personal effect.
Example 9
Original:
The organization internalized the new policy.
Alternative:
The organization incorporated the new policy into its procedures.
Why it works:
Incorporated is more concrete for organizational processes.
Example 10
Original:
It took time for her to internalize the lesson.
Alternative:
It took time for the lesson to sink in.
Why it works:
Sink in is more conversational and focuses on gradual understanding.
Comparison of Synonyms for Internalize
| Phrase | Tone | Meaning / Scope | Best Use | Example |
|---|---|---|---|---|
| Internalize | Neutral/formal | Make an idea part of your thinking or behavior | General | She internalized the lesson. |
| Absorb | Neutral | Take in information or ideas | Education | He absorbed the new information. |
| Assimilate | Formal | Incorporate knowledge into existing understanding | Academic | Students assimilated the concepts. |
| Incorporate | Professional | Make something part of an existing whole | Business | We incorporated the feedback. |
| Integrate | Formal | Combine with an existing system or process | Professional | They integrated the new method. |
| Adopt | Neutral/formal | Accept and begin using something | Business | The team adopted the approach. |
| Embrace | Expressive | Accept willingly or enthusiastically | Personal/professional | She embraced the new idea. |
| Take to heart | Conversational | Let advice or criticism affect you | Personal | He took the advice to heart. |
| Apply | Neutral | Use knowledge or principles | Education/work | Apply what you learned. |
| Take in | Casual/neutral | Understand or absorb information | Everyday | She took in the information. |
| Embed | Formal | Establish firmly in a system or habit | Corporate | The program embedded good practices. |
| Let it sink in | Casual | Give yourself time to understand | Conversation | Let the information sink in. |
Which Alternative Should You Choose?
For Formal Writing
Choose assimilate, incorporate, integrate, adopt, or embed, depending on the exact meaning.
For Business Communication
Choose adopt, incorporate, integrate, apply, or put into practice.
For Academic Writing
Choose assimilate, absorb, understand, integrate, or apply.
For Legal Writing
Choose the precise term that describes the documented action, such as adopt, incorporate, implement, or comply with where appropriate.
For Professional Email
Use review, consider, take on board, incorporate, apply, or put into practice.
For Everyday Conversation
Use take in, learn, understand, take to heart, or let it sink in.
For Casual Messages
Use get it, take it in, let it sink in, or make it your own when the context supports them.
Grammar and Usage Guide
How to Use Internalize as a Verb
Internalize is normally a transitive verb, meaning it usually takes an object.
Correct:
She internalized the lesson.
He internalized the criticism.
They internalized the company’s values.
Common Patterns
The most common structure is:
Subject + internalize + object
Students internalized the concepts.
Another useful structure is:
Subject + internalize + idea/belief/value/lesson
She internalized the belief that practice matters.
Internalize vs. Internalise
Internalize is the standard American English spelling.
Internalise is commonly used in British English.
Since this article uses American English, internalize is preferred.
Internalized
The past tense and past participle are:
internalized
Example:
The team internalized the lessons from the project.
Internalizing
The -ing form is:
internalizing
Example:
Internalizing new information can take time.
Internalization
The noun form is:
internalization
Example:
The internalization of these values happened gradually.
Avoid Unnecessary Prepositions
Instead of:
She internalized into the new system.
Use:
She integrated the new information into her existing knowledge.
Internalize itself normally does not require into in this construction.
Common Mistakes to Avoid
1. Treating Every Alternative as an Exact Synonym
Absorb, adopt, and take to heart have different shades of meaning.
Choose based on context.
2. Using “Understand” When Deep Acceptance Is Intended
He understood the principle.
does not necessarily mean:
He internalized the principle.
Understanding describes comprehension; internalization suggests deeper integration.
3. Using “Adopt” for Emotional Processing
Adopt works well for beliefs, methods, and policies, but it may not accurately describe processing an emotional experience.
4. Using Casual Expressions in Formal Writing
Phrases such as get it and let it sink in may sound too informal in academic or corporate documents.
5. Using Overly Formal Vocabulary
Inculcate can be accurate, but it may sound unnecessarily complicated when teach or develop would be clearer.
6. Confusing Learning With Application
Learning something and applying it are different.
She learned the procedure.
does not necessarily mean:
She applied the procedure correctly.
7. Ignoring the Audience
A phrase that sounds natural in conversation may sound inappropriate in a research paper.
8. Making the Sentence More Complicated Than Necessary
If learn communicates the idea clearly, there is no need to replace it with a highly formal word.
When Not to Use “Internalize”
When You Simply Mean “Learn”
If the idea only involves gaining information, learn may be clearer.
Students learned the new vocabulary.
When You Mean “Use”
If the main point is practical application, use apply or put into practice.
When You Mean “Accept”
If someone simply agrees with or recognizes something, accept may be more accurate.
When You Mean “Understand”
If there is no suggestion of deeper integration, understand is usually simpler.
When the Audience Needs Plain English
For general readers, phrases such as learn, understand, use, and take in may be easier to understand.
When a More Specific Word Exists
Instead of:
The company internalized the feedback.
consider:
The company incorporated the feedback into its policy.
The second sentence tells the reader exactly what happened.
When “Internalize” Is Actually the Better Choice
Keep internalize when you mean that an idea, value, belief, lesson, or experience has become part of someone’s way of thinking or behaving.
Over time, she internalized the principle of treating mistakes as opportunities to learn.
Here, the word communicates a deeper change than simply understood.
Advanced Writer Tips
Tone Control
For a formal tone, use:
assimilate, integrate, incorporate, embed
Neutral tone, use:
absorb, learn, adopt, understand
For a conversational tone, use:
take in, take to heart, let it sink in
Professional Email Etiquette
Professional writing is usually stronger when you describe the specific action you want.
Instead of:
Please internalize the new guidelines.
Try:
Please review the new guidelines and apply them to your next project.
This tells the reader exactly what to do.
Politeness
Small wording changes can make a request feel less demanding.
Take our feedback to heart.
can sound personal.
Please consider our feedback.
is softer and more neutral.
Context Alignment
Ask yourself what actually happened:
- Did someone learn something?
- Did they accept it?
- Did they adopt it?
- Did they apply it?
- Did they incorporate it?
- Did it become deeply rooted in their thinking?
The answer will usually reveal the best alternative.
Precision
Do not choose a synonym because it sounds sophisticated. Choose it because it describes the action accurately.
Readability
Short, familiar words often improve clarity.
Employees learned the new process.
is easier to understand than:
Employees assimilated the newly introduced procedural framework.
Use advanced vocabulary only when it adds useful precision.
Related Questions About Internalize
What Is Another Way to Say Internalize?
Depending on the context, you can say absorb, assimilate, incorporate, integrate, adopt, embrace, take in, take to heart, apply, or make your own.
What Is a Professional Alternative to Internalize?
Incorporate, integrate, adopt, assimilate, and apply are useful professional alternatives. The correct choice depends on whether you mean acceptance, understanding, or practical use.
What Is a Formal Alternative to Internalize?
Assimilate, incorporate, integrate, embed, and inculcate can work in formal contexts, but they are not interchangeable.
What Can I Use Instead of Internalize?
Use absorb for information, adopt for ideas or methods, take to heart for advice, incorporate for feedback or elements, and apply for knowledge or principles.
Is Internalize a Formal Word?
Internalize is a standard neutral-to-formal word. It is common in academic, psychological, educational, professional, and personal-development contexts.
Can I Use “Absorb” Instead of “Internalize”?
Sometimes. Absorb is especially suitable for information or knowledge. However, internalize can suggest a deeper change in thinking, belief, or behavior.
What Is the Difference Between Internalize and Adopt?
Adopt usually means accepting or beginning to use an idea, method, policy, or belief. Internalize suggests that something has become more deeply integrated into someone’s thinking, values, or behavior.
FAQs
Is “internalize” a synonym for “learn”?
They overlap, but they are not identical. Learn means gaining knowledge or skill, while internalize suggests that the knowledge, idea, or lesson becomes part of someone’s thinking or behavior.
What is the closest synonym for internalize?
There is no single perfect replacement for every context. Absorb, assimilate, incorporate, and integrate are among the closest alternatives, depending on what is being internalized.
Is “absorb” more informal than “internalize”?
Usually, absorb is more neutral and flexible. It works well in both everyday and professional writing, while internalize can sound more analytical or formal.
What is the opposite of internalize?
Depending on the context, possible opposites include reject, externalize, disregard, dismiss, or fail to absorb. The correct opposite depends on whether the original meaning involves beliefs, information, emotions, or behavior.
Can “embrace” replace “internalize”?
Sometimes. Embrace suggests willing acceptance, often with a positive attitude. Internalize focuses more on something becoming part of a person’s thinking or behavior.
Is “take to heart” the same as “internalize”?
They are similar when discussing advice, criticism, or lessons. Take to heart is more conversational and emphasizes personal or emotional impact.
Is “incorporate” a good synonym for internalize?
It can be, especially when something is added to an existing system, process, or body of knowledge. However, incorporate does not necessarily imply a personal psychological change.
Key Takeaways
- Internalize means making an idea, lesson, belief, or experience part of your thinking or behavior.
- Absorb and assimilate work especially well for learning and information.
- Adopt and embrace emphasize accepting an idea, belief, method, or value.
- Incorporate and integrate are useful when something becomes part of an existing system or process.
- Always choose the alternative that matches the exact meaning, audience, tone, and context.
Conclusion
Choosing the right synonym for internalize depends on what you mean by the word. If you are talking about learning information, absorb or assimilate may be more accurate. If you mean accepting a belief or method, adopt or embrace can work. For professional writing, incorporate, integrate, and apply often provide clearer descriptions of what actually happens.
For personal advice or criticism, take to heart is a natural conversational choice, while let it sink in works well when emphasizing gradual understanding. The key is not to replace internalize mechanically. First identify whether the situation involves learning, accepting, applying, integrating, or emotionally processing something. Then choose the word that expresses that specific idea clearly and naturally.