[ breyn ]
/ breɪn /
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See synonyms for: brain / brained / braining / brains on Thesaurus.com

verb (used with object)
to smash the skull of.
Slang. to hit or bang (someone) on the head.
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Idioms about brain

Origin of brain

First recorded before 1000; Middle English; Old English bræg(e)n, bregen; cognate with Low German brägen, Dutch brein; akin to Greek brégma; see bregma

synonym study for brain

3. See mind.


brainlike, adjectivesu·per·brain, noun
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023


What is a basic definition of brain?

The brain is the organ in humans and animals that’s responsible for thought processes. The plural form brains refers to intelligence or a person who is the smartest member of a group. The word brain has several other senses as a noun and a few as a verb.

Your brain is a squishy organ located inside your head and is protected by your skull. The brain is highly complex. It is the seat of all your conscious thoughts and unconscious impulses and is like the control center of the body, allowing you to do things like speak, move your muscles, and breathe without thinking. The brain, spinal cord, and nerves make up the nervous system.

Real-life examples: You and every other person have a brain. Animals have brains too, although they aren’t capable of doing all of the things the human brain is able to do. Your brain is very important and has a vast number of jobs, such as keeping all of your memories, telling your other organs what to do, and helping you read these words.

Used in a sentence The brain is the most complex and perhaps the most studied organ.  

The plural form brains is used as a term for intelligence or intellect. This usage alludes to the brain being the organ that handles thinking.

Real-life examples: You may have heard a person being described as having brains. This means they are smart and able to figure things out, especially difficult or complex problems.

Used in a sentence: I have to study hard to do well in math, but my sister has brains and aces her tests without studying. 

Relatedly, a person who is considered very smart can be called a brain.

Used in a sentence: None of us could figure out the computer problem so we called in Mike, who was a real brain when it comes to fixing them. 

Brains is also used to refer to the smartest member or members of a group or team, especially the one who comes up with plans.

Real-life examples: Movies and shows that feature a heist or a plan often have a person who is referred to as the “brains of the operation.” For example, scientist Bruce Banner often comes up with plans or solutions for the Avengers (when he isn’t getting angry and turning into the Incredible Hulk). In the Harry Potter series, Hermione is definitely the brains of the trio that she forms with Harry and Ron.

Used in a sentence: Everyone knew that Edd was the real brains behind the money-making schemes.

Where does brain come from?

The first records of brain come from before the year 1000. It comes from the Old English brægen (“brain”). This term is related to other words for brain, such as the Old Frisian brein, the Middle Low German brēgen, and Greek brekhmos (“forehead”).

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What are some other forms related to brain?

  • brainlike (adjective)
  • superbrain (noun)

What are some synonyms for brains?

What are some words that share a root or word element with brain

What are some words that often get used in discussing brain?

How is brain used in real life?

Brain is a common word that refers to either the organ in your skull or your intellect.



Try using brain!

True or False?

Someone who is described as having brains is usually someone who is very smart.

How to use brain in a sentence

British Dictionary definitions for brain

/ (breɪn) /

verb (tr)
to smash the skull of
slang to hit hard on the head

Word Origin for brain

Old English brægen; related to Old Frisian brein, Middle Low German bregen, Greek brekhmos forehead
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for brain

[ brān ]

The part of the nervous system in vertebrates that is enclosed within the skull, is connected with the spinal cord, and is composed of gray matter and white matter. It is the control center of the central nervous system, receiving sensory impulses from the rest of the body and transmitting motor impulses for the regulation of voluntary movement. The brain also contains the centers of consciousness, thought, language, memory, and emotion. See more at brainstem cerebellum cerebrum.
A bundle of nerves in many invertebrate animals that is similar to the vertebrate brain in function and position.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Cultural definitions for brain


The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Other Idioms and Phrases with brain


The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.