People use many expressions to describe a close friend. Some call that person a best friend, while others use phrases such as partner in crime, thick as thieves, joined at the hip, or a friend through thick and thin.
These expressions may appear similar, but they do not all work in the same way. Some are idioms, while others are synonyms or alternative words for a best friend.
The main difference is simple:
An idiom for a best friend expresses friendship through a figurative phrase, while a synonym directly names a close friend using another word or expression.
For example:
- Partner in crime is an idiomatic expression for a very close friend.
- Companion is a synonym or related word for a friend.
Idioms often create a stronger image, emotion, or personality. Synonyms usually communicate the meaning more directly. Understanding this difference helps students, writers, and ESL learners choose expressions that sound natural and accurate.
What Idioms for Best Friend Mean
An idiom for a best friend is a fixed or commonly used expression that describes a close friendship in a figurative way.
The literal meaning of the words may differ from the intended meaning.
For example:
Maya and I have been thick as thieves since childhood.
This sentence does not mean that Maya and the speaker are thieves. The expression means they are extremely close and often share secrets or experiences.
Simple definition
An idiom for a best friend is a figurative phrase used to describe a loyal, close, or long-lasting friendship.
Purpose
These idioms help speakers and writers:
- express affection
- show loyalty
- describe a strong emotional bond
- make writing more vivid
- add humor or personality
- avoid repeating “best friend”
How it works
An idiom works as a complete expression. Its meaning comes from the phrase as a whole rather than from the literal definitions of its individual words.
Short example
Daniel has always been my rock.
Here, “rock” means a dependable and supportive friend.
Why it gets confused with synonyms
Idioms and synonyms can communicate similar ideas. However, a synonym gives a direct alternative, while an idiom expresses the idea figuratively.
What Synonyms for Best Friend Mean
A synonym for best friend is a word or direct expression with a similar meaning to “best friend.”
Common examples include:
- close friend
- companion
- confidant
- bestie
- lifelong friend
- trusted friend
- closest friend
- dear friend
These alternatives differ slightly in tone and meaning. For instance, a confidant is someone you trust with private information, while a companion is someone who regularly spends time with you.
Simple definition
A synonym for best friend is a word or direct phrase that names someone who shares a close and trusted relationship with another person.
Purpose
Synonyms help writers and speakers:
- avoid unnecessary repetition
- choose the right level of formality
- describe a friendship more precisely
- match the tone of a conversation or text
- clarify the type of relationship
How it works
A synonym usually replaces “best friend” directly in a sentence, although the exact meaning may change slightly.
Short example
Aisha is my closest confidant.
The word “confidant” directly identifies a trusted person.
Why it gets confused with idioms
Some multiword synonyms look like idioms. Expressions such as “lifelong friend” and “closest companion” contain more than one word, but their meanings remain direct rather than figurative.
Idioms for Best Friend vs Synonyms for Best Friend: The Core Difference
Idioms and synonyms can both describe close friendship, but they do so differently.
An idiom uses figurative or nonliteral language.
A synonym uses a direct alternative word or phrase.
Compare these examples:
Noah is my partner in crime.
“Partner in crime” is an idiom. It often refers playfully to a close friend who joins you in adventures or harmless mischief.
Noah is my closest companion.
“Closest companion” is a direct description. It does not depend on a figurative meaning.
Idioms tend to sound more expressive, informal, and imaginative. Synonyms tend to sound clearer, more flexible, and easier to use in formal writing.
Quick Comparison Table
| Point | Idioms for Best Friend | Synonyms for Best Friend |
|---|---|---|
| Definition | Figurative expressions describing a close friend | Direct words or phrases with a similar meaning |
| Scope | Usually expresses a particular quality of friendship | Broadly names or describes a close friend |
| Purpose | Adds emotion, imagery, humor, or personality | Provides clarity, variety, and precision |
| Length | Often consists of several words | Can be one word or a short phrase |
| Structure | Usually functions as a fixed expression | Works as a replaceable noun or noun phrase |
| Meaning | Often nonliteral or symbolic | Usually direct and literal |
| Use in writing | Useful in dialogue, stories, captions, and informal writing | Useful in formal, informal, academic, and everyday writing |
| Example | “We are joined at the hip.” | “She is my closest companion.” |
| Tone | Expressive and often conversational | Depends on the chosen word |
| Difficulty for learners | Can be difficult because the meaning is not literal | Usually easier to understand |
How Idioms for Best Friend Work
Idioms describe friendship through familiar images or cultural expressions.
Consider the idiom:
We have been through thick and thin together.
The phrase refers to remaining loyal during both easy and difficult times. “Thick” and “thin” do not literally describe the friendship. Together, the words create a recognized figurative meaning.
Many friendship idioms focus on one of the following qualities:
Loyalty
Expressions such as through thick and thin emphasize support during difficult situations.
Closeness
Idioms such as joined at the hip suggest that two friends spend a great deal of time together.
Trust
An expression such as my rock describes someone dependable and emotionally supportive.
Shared experiences
The phrase partner in crime often describes someone who joins in adventures, jokes, or playful behavior.
Similarity
The idiom two peas in a pod describes two people who are very similar or spend a lot of time together.
Idioms work best when the listener understands the figurative meaning. Without that knowledge, the phrase may sound strange or confusing.
How Synonyms for Best Friend Work
Synonyms describe the person or relationship directly. They allow the speaker to choose a word based on the exact type of friendship.
For example:
Lena is my confidant.
1-This word emphasizes trust and private communication.
Lena is my companion.
2-This word emphasizes shared time or activities.
Lena is my bestie.
3-This word sounds casual, warm, and modern.
Lena is my lifelong friend.
This phrase emphasizes the length of the friendship.
Not every synonym carries the full meaning of “best friend.” A companion may not necessarily be someone’s closest friend. A confidant may provide emotional trust without spending much time with the person.
For that reason, writers should choose synonyms based on context rather than treating every related word as completely interchangeable.
Key Differences in Simple Language
The easiest way to separate idioms from synonyms is to ask whether the expression means exactly what its words normally mean.
If the answer is no, it is probably an idiom.
For example:
We are thick as thieves.
The phrase does not literally describe body thickness or criminal behavior. It figuratively means that two people are extremely close.
Now compare it with:
We are close friends.
Every word keeps its normal meaning. This is a direct phrase rather than an idiom.
Another important difference involves replacement.
A synonym often fits into the same grammatical position as “best friend”:
He is my best friend.
He is my closest companion.
An idiom may require the entire sentence to change:
He is my best friend.
We are joined at the hip.
Therefore, synonyms are often easier to substitute, while idioms may need a different sentence structure.
Can Idioms and Synonyms Overlap?
Idioms and synonyms can overlap in meaning, but they remain different types of language.
For example, both of these sentences describe a close friend:
Rachel is my bestie.
Rachel is my partner in crime.
“Bestie” is an informal synonym for best friend. “Partner in crime” is an idiom.
The two expressions overlap because both refer to a close relationship. However, “partner in crime” adds an extra suggestion of shared adventures, playful trouble, or mischief.
Some expressions sit near the boundary between idioms and descriptive phrases. Kindred spirit, for example, can function figuratively because it refers to someone who shares similar values, feelings, or interests. In everyday use, it may also act as a direct label for a deeply compatible friend.
Context usually reveals how the expression works.
Examples of Idioms for Best Friend
1. Partner in crime
Meaning: A close friend who joins you in adventures or playful mischief.
Example:
Sophie has been my partner in crime since university.
This expression sounds friendly and humorous. It does not usually suggest real criminal activity.
2. Through thick and thin
Meaning: Remaining loyal during both good and difficult times.
Example:
He stayed beside me through thick and thin.
This idiom emphasizes loyalty rather than simply closeness.
3. Two peas in a pod
Meaning: Two people who are very similar or nearly always together.
Example:
Mia and Chloe are like two peas in a pod.
Writers often use this idiom for friends who share similar personalities, habits, or interests.
4. Joined at the hip
Meaning: Spending nearly all your time together.
Example:
The two friends have been joined at the hip all summer.
The phrase exaggerates physical closeness to describe a strong friendship.
5. My rock
Meaning: A dependable person who provides emotional support.
Example:
During the hardest year of my life, Emma was my rock.
This idiom focuses on strength, stability, and support.
6. Thick as thieves
Meaning: Extremely close, often sharing secrets.
Example:
The cousins became thick as thieves during the holidays.
The phrase can describe close friends, siblings, relatives, or colleagues.
7. Have each other’s backs
Meaning: Support and protect one another.
Example:
We may disagree sometimes, but we always have each other’s backs.
This idiom highlights mutual loyalty.
8. A shoulder to cry on
Meaning: Someone who listens and offers comfort during emotional moments.
Example:
She has always given me a shoulder to cry on.
The expression refers to emotional support rather than physical crying alone.
9. Cut from the same cloth
Meaning: Very similar in personality, behavior, or values.
Example:
Marcus and Ben are clearly cut from the same cloth.
This phrase can describe friends who think or behave alike.
10. Birds of a feather
Meaning: People with similar interests or personalities who naturally spend time together.
Example:
They became friends quickly because birds of a feather flock together.
The shorter phrase “birds of a feather” may also describe similar people.
11. Kindred spirit
Meaning: Someone who shares your values, interests, or way of thinking.
Example:
I knew from our first conversation that she was a kindred spirit.
This expression often suggests a deep intellectual or emotional connection.
12. Go way back
Meaning: To have known someone for a long time.
Example:
Daniel and I go way back.
This informal idiom works well when describing old friends.
13. In the same boat
Meaning: Experiencing the same situation or difficulty.
Example:
We became close because we were both in the same boat.
This idiom does not always mean “best friend,” but it can explain how a friendship developed.
14. Know someone inside out
Meaning: Understand someone’s personality, habits, and feelings extremely well.
Example:
My best friend knows me inside out.
This expression highlights deep familiarity.
15. Like family
Meaning: So close that the person feels like a family member.
Example:
After twenty years of friendship, Nina is like family to me.
This is a common and natural way to express emotional closeness.
Examples of Synonyms for Best Friend
1. Close friend
A person with whom someone shares a strong personal relationship.
Aaron is one of my closest friends.
2. Bestie
An informal and affectionate word for a best friend.
I am meeting my bestie after class.
This word works well in casual speech, messages, and social media captions.
3. Companion
A person who spends time with someone or shares activities with them.
She became his trusted travelling companion.
“Companion” can sound slightly more formal than “friend.”
4. Confidant
A person trusted with private thoughts, feelings, or secrets.
My sister has always been my closest confidant.
The traditionally masculine spelling is confidant, while confidante has historically referred to a woman. Modern English often uses “confidant” for any gender.
5. Trusted friend
A friend who can be relied upon.
He discussed the decision with a trusted friend.
This phrase sounds clear and professional.
6. Lifelong friend
A person who has remained a friend for much of someone’s life.
Olivia is a lifelong friend from primary school.
7. Dear friend
A friend for whom someone feels strong affection.
I received a letter from a dear friend.
This phrase may sound warm, sincere, or slightly formal.
8. Closest friend
The person with whom someone shares the strongest friendship.
She is my closest friend at work.
9. Old friend
Someone known for a long time.
I met an old friend for lunch.
“Old friend” usually refers to the length of the relationship, not the person’s age.
10. Childhood friend
A person who became a friend during childhood.
He opened the business with a childhood friend.
11. Soulmate
A person with whom someone feels a powerful emotional connection.
She describes her best friend as her platonic soulmate.
“Soulmate” often refers to romantic love, so adding “platonic” can prevent confusion.
12. Ally
A person who supports someone, especially during conflict or difficulty.
She became an important friend and ally.
An ally may support someone without being their best friend.
13. Mate
An informal word for friend, especially common in British, Australian, and New Zealand English.
He is one of my closest mates.
14. Buddy
A casual word for a friend.
I went hiking with my college buddy.
“Buddy” does not always imply a very deep friendship.
15. Pal
An informal word for friend.
She is an old pal of mine.
“Pal” often sounds friendly and casual, though its popularity varies by region.
Idioms vs Synonyms in Literature and Writing
Writers use idioms and synonyms for different purposes.
Idioms can reveal a character’s personality, background, mood, or speaking style. A character who says, “She is my partner in crime,” may sound playful and relaxed. A character who says, “She has been my rock,” may sound grateful or emotionally vulnerable.
Synonyms give writers greater precision.
Consider these sentences:
Henry was her companion.
This may suggest shared time or travel.
Henry was her confidant.
This suggests private trust.
Henry was her childhood friend.
This emphasizes history.
Henry was her closest ally.
This emphasizes support during conflict.
Each word changes the reader’s understanding of the relationship.
In formal essays, reports, and academic writing, direct alternatives usually work better than highly conversational idioms. In fiction, memoir, dialogue, personal essays, and social media writing, idioms can make the language warmer and more memorable.
Writers should also consider whether an idiom matches the character, setting, and time period. A very modern expression may sound unnatural in a historical story unless the narrator uses modern language deliberately.
Idioms vs Synonyms for Students and ESL Learners
Students and ESL learners often find synonyms easier because the words usually have direct meanings.
Idioms require more attention because translating them word for word may produce an incorrect meaning.
For example, an English learner may interpret “joined at the hip” literally. In normal conversation, however, it means that two people spend nearly all their time together.
A useful learning method includes three steps:
Learn the full expression
Do not memorize only one word from an idiom. Learn the entire phrase.
Correct:
through thick and thin
Not useful:
thick and thin as separate words
Learn the situation
Connect the idiom with the type of friendship it describes.
- My rock: support
- Partner in crime: shared adventures
- Two peas in a pod: similarity
- Joined at the hip: constant closeness
- Through thick and thin: loyalty
Learn a complete example
A full sentence shows grammar, tone, and natural usage.
Lucy supported me through thick and thin.
Students should also notice register. “Bestie” fits casual conversation, but “trusted friend” may fit a school essay or formal speech more naturally.
Common Mistakes and Confusion
Treating every friendship phrase as an idiom
Not every multiword expression is an idiom.
“Close friend” is a direct phrase. Its meaning comes from the ordinary meanings of “close” and “friend.”
“Thick as thieves” is an idiom because its intended meaning is not fully literal.
Assuming every synonym means exactly the same thing
Synonyms often share a general meaning without being identical.
A confidant emphasizes trust.
A companion emphasizes company.
An ally emphasizes support.
A childhood friend emphasizes history.
Choose the word that expresses the exact relationship.
Using “partner in crime” in a serious legal context
This phrase usually sounds playful when used for friends. However, in a discussion about real criminal activity, it may carry a literal meaning. Context matters.
Using informal words in formal writing
Words such as “bestie,” “buddy,” and “pal” may sound too casual in formal essays or professional documents.
Use alternatives such as:
- close friend
- trusted friend
- longtime companion
- confidant
Overusing idioms
One idiom can make a sentence lively. Too many can make writing sound forced or unclear.
Instead of writing:
My partner in crime, who is my rock and my shoulder to cry on, has been with me through thick and thin because we are two peas in a pod.
Choose the most relevant expression:
My best friend has been my rock during every difficult period.
Translating idioms literally
Idioms often lose their meaning in direct translation. Learners should study their actual use rather than translating each word separately.
Confusing “confidant” with “confident”
A confidant is a trusted person.
Confident means certain or self-assured.
Correct:
She is my closest confidant.
Correct:
She feels confident about the exam.
When to Use Idioms and When to Use Synonyms
Use an idiom when you want to:
- sound expressive or conversational
- add emotion or personality
- describe a specific friendship quality
- create a memorable image
- write dialogue, captions, stories, or personal messages
Example:
Happy birthday to my partner in crime!
Use a synonym when you want to:
- communicate clearly and directly
- avoid repeating “best friend”
- write formally
- describe the relationship precisely
- choose a word that matches a particular context
Example:
I discussed the matter with a trusted friend.
In many cases, you can combine direct and figurative language:
My closest friend has always been my rock.
“Closest friend” identifies the relationship directly, while “my rock” explains the type of support that person provides.
Related Terms People Often Confuse With Them
Metaphor
A metaphor describes one thing as another to create a comparison.
My best friend is my anchor.
This metaphor suggests that the friend provides stability. It may become idiomatic if people use it frequently as a recognized expression.
Simile
A simile compares two things using “like” or “as.”
We are like two peas in a pod.
“Two peas in a pod” often appears as part of a simile.
Nickname
A nickname is an informal name given to a person.
I call my best friend Bee.
A nickname does not describe the relationship unless the name itself carries that meaning.
Term of endearment
A term of endearment expresses affection.
Examples include:
- dear
- sweetheart
- love
- bestie
Some terms of endearment can refer to friends, family members, or romantic partners.
Collocation
A collocation is a group of words that commonly appear together.
Examples include:
- close friend
- lifelong friend
- trusted companion
- loyal friend
These combinations sound natural, but they are not necessarily idioms.
Proverb
A proverb expresses a general truth or piece of advice.
A friend in need is a friend indeed.
This proverb means that a true friend proves their loyalty during difficult times. It discusses friendship but does not directly serve as a synonym for “best friend.”
Slang
Slang consists of highly informal words and expressions.
Words such as “bestie,” “bro,” “sis,” and “BFF” may function as slang or casual labels for a close friend.
Conclusion
Idioms for a best friend and synonyms for a best friend both describe close relationships, but they serve different purposes.
Idioms communicate friendship through figurative language. Expressions such as partner in crime, my rock, two peas in a pod, and through thick and thin create emotion, imagery, and personality.
Synonyms communicate the relationship more directly. Words and phrases such as confidant, companion, bestie, lifelong friend, and trusted friend help speakers describe the exact nature of a friendship.
The simplest rule is this:
Use an idiom when you want expressive, figurative language. Use a synonym when you want a direct and precise alternative to “best friend.”
Both forms can improve speaking and writing when they match the context, tone, and intended meaning.
FAQs
What is a good idiom for a best friend?
“Partner in crime” is a popular idiom for a close friend who shares adventures, jokes, or playful experiences with you. “My rock” works better for a loyal and supportive friend.
Is “bestie” an idiom?
No. “Bestie” is an informal synonym or shortened form of “best friend.” Its meaning is direct rather than figurative.
What does “through thick and thin” mean in friendship?
It means staying loyal and supportive during both good times and difficult periods.
Is “two peas in a pod” used for best friends?
Yes. It describes two people who are very similar, very close, or frequently together. It can refer to best friends, siblings, partners, or relatives.
What is a formal synonym for best friend?
Suitable formal alternatives include “close friend,” “trusted friend,” “closest companion,” and “confidant.” The best choice depends on the context.
Can “soulmate” describe a best friend?
Yes. A person may describe a best friend as a soulmate when they share a deep emotional connection. The phrase “platonic soulmate” makes the non-romantic meaning clearer.
What is the difference between a confidant and a best friend?
A confidant is someone trusted with private thoughts or secrets. A best friend may also be a confidant, but the two terms are not identical. Someone can trust a confidant deeply without considering that person their closest overall friend.