brain

1 of 2

noun

ˈbrān 

1

a

: the portion of the vertebrate central nervous system enclosed in the skull and continuous with the spinal cord through the foramen magnum that is composed of neurons and supporting and nutritive structures (such as glia) and that integrates sensory information from inside and outside the body in controlling autonomic function (such as heartbeat and respiration), in coordinating and directing correlated motor responses, and in the process of learning compare forebrain, hindbrain, midbrain

b

: a nervous center in invertebrates comparable in position and function to the vertebrate brain

2

a(1)

: intellect, mind

has a clever brain

(2)

: intellectual endowment : intelligence

—often used in plural

plenty of brains in that family

b(1)

: a very intelligent or intellectual person

(2)

: the chief planner within a group

—usually used in plural

she's the brains behind their success

3

: something that performs the functions of a brain

especially : an automatic device (such as a computer) for control or computation

Illustration of brain

• 1 cerebral hemisphere
• 2 corpus callosum
• 3 ventricle
• 4 fornix
• 5 thalamus
• 6 pituitary gland
• 7 pons
• 8 medulla oblongata
• 9 spinal cord
• 10 cerebellum
• 11 midbrain

brain

2 of 2

verb

brained; braining; brains

transitive verb

1

: to kill by smashing the skull

2

: to hit on the head

Synonyms

Noun

• genius
• wizard
• intellect
• thinker

Examples of brain in a Sentence

Noun

Scientists are learning more about how the human brain works.

The left and right sides of the brain have different functions.

The other children always teased him about being such a brain.

Verb

The tree limb fell and nearly brained me.

Recent Examples on the Web

Noun

Increases Blood Potassium Levels Your body needs potassium for kidney, heart, muscle, and brain functions. —Merve Ceylan, Health, 8 July 2025

One problem is that in most organization, knowledge is spread around in many systems, brains and silos. —Stephen Diorio, Forbes.com, 8 July 2025

Verb

Fielder, in typical fashion, takes hair brained ideas to the extreme. —Matt Shaw, Forbes.com, 28 June 2025

Introduction May 7, 2025 biology brains cells memory molecular biology neurons neuroscience proteins All topics (opens a new tab) When Todd Sacktor (opens a new tab) was about to turn 3, his 4-year-old sister died of leukemia. —Ajdina Halilovic, Quanta Magazine, 7 May 2025

Word History

Etymology

Noun

Middle English, from Old English brægen; akin to Middle Low German bregen brain, and perhaps to Greek brechmos front part of the head

First Known Use

Noun

before the 12th century, in the meaning defined at sense 1a

Verb

14th century, in the meaning defined at sense 1

Phrases Containing brain

• acquired brain injury
• blood-brain barrier
• brain attack
• brain coral
• brain cramp
• brain-dead
• brain death
• brain drain
• brain dump
• brain fog
• brain freeze
• brain hormone
• brain-picking
• brain stem
• brain trust
• brain wave
• chemo brain
• half a brain
• left brain
• minimal brain dysfunction
• one's brain turns into/to mush
• on the brain
• organic brain syndrome
• pick someone's brain/brains
• rack one's brain
• right brain
• split-brain
• traumatic brain injury

Rhymes for brain

• ane
• bane
• blain
• cane
• chaine
• cheyne
• deign
• drain
• fain
• fane
• feign
• gain

Kids Definition

brain

1 of 2 noun

ˈbrān 

1

a

: the portion of the central nervous system of vertebrate animals that is the organ of thought and the central control point for the nervous system, is enclosed within the skull, and is continuous with the spinal cord

b

: the main nervous center in an invertebrate animal

2

a

: intelligence sense 1

—often used in plural

plenty of brains in that family

b

: a very intelligent person

brainlike adjective

brain

2 of 2 verb

1

: to kill by smashing the skull

2

: to hit on the head

Medical Definition

brain

noun

ˈbrān 

1

: the portion of the vertebrate central nervous system enclosed in the skull and continuous with the spinal cord through the foramen magnum that is composed of neurons and supporting and nutritive structures (as glia) and that integrates sensory information from inside and outside the body in controlling autonomic function (as heartbeat and respiration), in coordinating and directing correlated motor responses, and in the process of learning see forebrain, hindbrain, midbrain

2

: a nervous center in invertebrates comparable in position and function to the vertebrate brain