brain

IPA/breɪn/
KK[brˈen]IPA/breɪn/

brain — noun

  • brainsingular
  • brainsplural

1. the soft organ in your skull that lets you think, remember, feel, and control mo

1.nounA2
Definition

the soft organ in your skull that lets you think, remember, feel, and control movement.

Example

Doctors used a scan to check Mei's brain after the crash.

brain in a medical scan context

A hard fall from the bike caused swelling in Yusuf's brain.

Common collocations
  • brain scan
  • brain injury
  • brain tumor
  • brain surgery
  • brain damage
Synonyms
  • cerebrum

    technical and narrower; it can refer to only part of the brain.

  • grey matter

    informal and often used jokingly or figuratively.

  • mind

    usually means thoughts, not the physical organ itself.

Usage Note

Common with medical and body words such as 'scan', 'injury', 'tumor', and 'surgery'. Distinguish from sense 2: this sense names the physical organ, while sense 2 is about mental power.

2. mental strength for understanding things, learning fast, and working out problem

2.nounC1
Definition

mental strength for understanding things, learning fast, and working out problems.

Example

Noa has the brains to solve the puzzle before anyone else.

have the brains to + verb

Use your brain and read the safety sign before touching the wire.

use your brain for practical thinking

Common collocations
  • have brains
  • use your brain
  • brain power
  • a good brain
  • brain not muscle
Synonyms
  • intelligence

    the most neutral formal noun for mental ability.

  • intellect

    slightly more formal and often stresses serious thinking.

  • smarts

    informal and common in everyday speech.

  • brainpower

    stresses mental effort used to solve a task.

Antonyms
  • stupidity

    lack of good judgment or intelligence.

Grammar Patterns

have brains

use your brain

brain not muscle

Usage Note

Often appears in fixed expressions such as 'have brains' and 'use your brain'. Distinguish from sense 3: this sense is the quality itself, not a person who has it.

Common Mistakes

Aiko is brains.
Aiko has brains.
bare 'brains' refers to intelligence, not directly to a person.
Use your brains before you cross the road.
Use your brain before you cross the road.
singular is more usual in this fixed instruction.

3. a person thought to be very smart, especially in study or technical work.

3.nounC1
Definition

a person thought to be very smart, especially in study or technical work.

Example

Everyone called Ravi a brain after he fixed the school robot.

a brain = a very clever person

The company brought in two young brains to improve its phone app.

plural: brains for clever people

Common collocations
  • a real brain
  • young brains
  • local brains
  • one of the brains in the team
Synonyms
  • genius

    stronger; suggests extremely high natural ability.

  • intellectual

    often used for someone interested in serious ideas and study.

  • egghead

    informal and can sound mocking.

  • whiz

    informal; often used for someone excellent in one area such as math or computers.

Grammar Patterns

be a brain

one of the brains

Usage Note

Often sounds slightly informal or teasing, and it is common in the plural for a group of very clever people. Distinguish from sense 4: a 'brain' here is simply a smart person, not necessarily the one leading a plan.

Common Mistakes

Kenji is brain in our class.
Kenji is a brain in our class.
singular countable use needs 'a'.

4. the person in a team or scheme who thinks up the plan and directs how it is carr

4.nounC1
Definition

the person in a team or scheme who thinks up the plan and directs how it is carried out.

Example

Police said Nadia was the brain behind the museum theft.

the brain behind + plan or crime

Although Sven spoke little, he was the brain of the whole campaign.

the brain of + group effort

Common collocations
  • the brain behind the plan
  • the brain of the operation
  • criminal brain
  • be the brain behind
Synonyms
  • mastermind

    the closest match, especially for clever planning.

  • strategist

    stresses long-term planning rather than overall control.

  • organizer

    broader and more practical; not always the smartest person.

  • ringleader

    used mainly for the leader of a wrong or illegal group.

Grammar Patterns

the brain behind + noun

the brain of + group / operation

Usage Note

Most often used with 'behind' or 'of' when naming the project, operation, or crime. Distinguish from sense 3: this sense highlights control and planning, not just intelligence.

Common Mistakes

Lior has the brain behind the plan.
Lior is the brain behind the plan.
this sense names the person responsible.
Mina was the brain for the robbery.
Mina was the brain behind the robbery.
'behind' is the usual preposition with this pattern.
Idioms

beat your brains out

idiom

To try very hard to think or understand something for a long time.

Mia beat her brains out trying to solve the math problem.

Did you beat your brains out studying for the exam?

blow your/somebody’s brains out

idiom

To kill yourself or another person by shooting them in the head.

The villain threatened to blow his brains out if the police came closer.

In the movie, the soldier blew his own brains out with a pistol.

cudgel your brains

idiom

To think very hard in order to remember or understand something.

Sara cudgeled her brains to recall the password.

He cudgeled his brains but couldn't remember the address.

have something on the brain

idiom

To think about something constantly, often in an annoying way.

Diego has video games on the brain and talks about them nonstop.

Why do you have money on the brain all the time?

pick somebody’s brains

idiom

To ask someone many questions because they know more about a topic than you do.

I need to pick your brains about fixing this computer.

Maya picked the professor's brains after the lecture.

rack your brain(s)

idiom

To think very hard or for a long time about something.

Aiden racked his brain for a good birthday gift idea.

We racked our brains but couldn't solve the puzzle.

brain — verb

Word family

Synonym discussion

Sense: noun/2

These words all relate to mental ability, but they are not used in exactly the same way. 'Brain' in this sense is fairly informal and often appears in short contrasts such as 'brain, not muscle' or in advice like 'use your brain'. 'Intelligence' is the most neutral and widest term; it works in everyday speech, education, and psychology. 'Intellect' is more formal and often suggests serious thought, reasoning, or academic life. 'Brains' is an informal plural form often heard in phrases like 'She has brains', especially when praising practical cleverness. 'Brainpower' stresses mental effort used to solve a difficult problem. You might say 'The job needs intelligence', 'The professor is known for her intellect', 'Noa has brains', and 'The team used all its brainpower to fix the software bug'.

brain ↗intelligence ↗intellect ↗brains ↗brainpower

Common collocations

Nouns

  • brain scan
  • brain injury
  • brain power
  • brain surgery

Phrases

  • use your brain
  • have brains
  • the brain behind
  • brain, not muscle

Prepositions

Etymology

Proto-GermanicOld EnglishEnglish

The word comes from Old English 'brægen', which already meant the organ in the head. It belongs to an old Germanic family of words for the brain, with related forms in some nearby languages such as Dutch and Low German. English has kept the basic physical meaning for over a thousand years, and later extended it naturally to mean intelligence, a clever person, and the planner in charge of a group.