brain

1 of 2

noun

ˈbrān

: 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

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

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

: 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

: to kill by smashing the skull

: to hit on the head

Example Sentences

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

The man was suffering from a bacterial infection that his blood was ferrying throughout his body, showering the infection to his brain and elsewhere, Masuda said. —

Emily Alpert Reyes, Los Angeles Times, 28 May 2023 In other words, the infection in a pimple on your nose has a somewhat clear path to your brain. —

Maggie O'neill, Health, 27 May 2023 And hey, any excuse for turning off your brain via a quick catnap is probably welcome. —

Lisa Bain, Good Housekeeping, 26 May 2023 Investigators analyze tissue from at least two locations in the animal’s brain, the CDC said on its website. —

Saleen Martin, USA TODAY, 26 May 2023 Chronic loneliness rewires our brains and produces harmful inflammation. —

Cindy Jordan, Fortune, 26 May 2023 The race against Elon Musk to put chips in people’s brains What is Neuralink? —

Faiz Siddiqui, Washington Post, 26 May 2023 And Donald Trump is in a courtroom in Manhattan testifying, lying his brains out, as will be obvious to everyone watching except the MAGA people. —

Michael Tomasky, The New Republic, 26 May 2023 That makes adolescents and young adults particularly vulnerable to the effects of cannabis as their brains continue to mature. —

Akshay Syal, M.d., NBC News, 26 May 2023

Verb

Companies will also have to make sure their chatbots create words and pictures that are truthful and respect intellectual property, and will be required to register their algorithms, the software brains behind chatbots, with regulators. —

Chang Che, New York Times, 24 Apr. 2023 So can brain injuries and tumors. —

Carl Zimmer, Discover Magazine, 4 Dec. 2014 Thanks to producer PJ Elliott for his great work on the show, and be sure to tune in tomorrow when PJ speaks with Health reporter, Karen Weintraub about the latest organ transplant milestone: pig hearts to brain dead patients. —

Taylor Wilson, USA TODAY, 13 July 2022 Internet connections can be wireless, so why shouldn’t brain medicine be? —

Elizabeth Preston, Discover Magazine, 2 Dec. 2015 The cancer initiative is personal for Biden, who lost his son Beau Biden to brain cancer in 2015. —

Alexander Thompson, BostonGlobe.com, 11 Sep. 2022 The man who could brain Mr. Lingk with Rusty’s ashes, or the one who could harm and tie up a helpless old lady, would almost certainly be game for something that nasty. —

Alan Sepinwall, Rolling Stone, 9 Aug. 2022 This can help alleviate back and neck stress and give your eyes and brain a break from the screen. —

Alexa Mikhail, Fortune, 28 July 2022 They are linked to brain developmental problems in infants and cancer. —

Katy Stech Ferek, WSJ, 31 Jan. 2022 See More

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'brain.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

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

Time Traveler

The first known use of brain was before the 12th century

See more words from the same century

Cite this Entry

Style

“Brain.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/brain. Accessed 8 Jun. 2023.

Copy Citation

Kids Definition

brain

1 of 2 noun

ˈbrān

: 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

: the main nervous center in an invertebrate animal

: intelligence sense 1

—often used in plural

plenty of brains in that family

: a very intelligent person

brainlike adjective

brain

2 of 2 verb

: to kill by smashing the skull

: to hit on the head

Medical Definition

brain

noun

ˈbrān

: 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

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