brain

noun
\ˈbrān \

Definition of brain 

(Entry 1 of 2)

1a : 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

2a(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

brain

verb
brained; braining; brains

Definition of brain (Entry 2 of 2)

transitive verb

1 : to kill by smashing the skull

2 : to hit on the head

Illustration of brain

Illustration of brain

Noun

brain 1a: 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

In the meaning defined above

Keep scrolling for more

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.
See More

Recent Examples on the Web: Noun

Grief and loss On Oct. 16, 2002, Reyes’ 22-month-old son, Tyler, died from a rare genetic disease that affected his brain development. Steve Miletich, The Seattle Times, "‘He’s just a doer’: Meet Seattle police-chief candidate Ely Reyes," 9 July 2018 One year ago this weekend, the six-term senator and former prisoner of war was diagnosed with glioblastoma, a deadly form of brain cancer. Yvonne Wingett Sanchez, azcentral, "A year after John McCain's cancer diagnosis, Cindy McCain expresses gratitude to caregivers," 13 July 2018 Her mom was out of surgery—but diagnosed with a fatal form of brain cancer. Colleen Leahey Mckeegan, Marie Claire, "The Business of Feeling Good," 11 July 2018 Republicans need to steer his nomination through the party’s narrow 51-49 Senate majority in which one Republican, Sen. John McCain of Arizona, is absent while battling brain cancer. Louise Radnofsky, WSJ, "Senate’s First Skirmish Over Supreme Court Pick Brett Kavanaugh: How Quickly to Move," 11 July 2018 One prominent Republican, John McCain, is expected to be unable to vote because of his ongoing battle with brain cancer. Gregg Re, Fox News, "Kavanaugh nod touches off Supreme Court confirmation battle; Dems warn of 'deaths of countless women'," 10 July 2018 Republicans hold a 51 vote majority, and Sen. John McCain R-Arizona is receiving treatment for brain cancer. Erica Martinson, Anchorage Daily News, "Lisa Murkowski is ‘annoyed’ with prejudging of Trump’s Supreme Court pick," 10 July 2018 The confirmation process promises to be a fight, and Republicans have a narrow 51-49 majority -- with almost no room to lose votes as Republican Sen. John McCain of Arizona remains absent while fighting brain cancer. Jennifer Jacobs And Mark Niquette, Houston Chronicle, "Trump making Supreme Court pick to cement conservative majority," 9 July 2018 With a 51-49 Senate Republican majority, and Sen. John McCain, R-Ariz., probably unable to participate because of brain cancer, Trump’s nominee will need support from every Republican if Democrats all vote in opposition. Bob Egelko, SFChronicle.com, "Trump has ‘outsourced’ his Supreme Court picks to this conservative group," 8 July 2018

Recent Examples on the Web: Verb

According to the study, the ratio of neurons to brain size in most carnivores was nearly equivalent to herbivores. Elly Belle, Teen Vogue, "Study Says Dogs Are Actually Smarter Than Cats," 18 June 2018 Took out Isadora Duncan when her scarf got caught in the spokes of a wheel, decapitated Jayne Mansfield, sprayed John Kennedy’s brains all over his wife. Aaron Gilbreath, Longreads, "The Red Caddy," 24 Apr. 2018 At least 64 people perished during the storm, drowned in their houses or brained by flying debris. The Economist, "America has let down its Puerto Rican citizens," 12 Apr. 2018 Yet if there’s a British stereotype of American English as twangy and slangy, there’s a corresponding American stereotype of British English as quaint and feather-brained. Henry Hitchings, WSJ, "‘The Prodigal Tongue’ Review: More Trouble in the Colonies," 12 Apr. 2018 Today’s condom challenge will morph into tomorrow’s equally hare-brained idea. Heidi Stevens, chicagotribune.com, "Calm down about the condom challenge, grown-ups," 2 Apr. 2018 Many experts believe that maintaining physical fitness can help keep blood flowing normally to brain tissue, which can reduce the risk of damage or deterioration. Amanda Macmillan, Time, "How Exercise May Help Protect Your Brain From Cognitive Decline and Dementia," 16 Feb. 2018 But Scotti falls back on the same old, tired, lizard-brained and misogynistic argument that people used against Hillary Clinton: That ambitious women are off-putting. Madeleine Aggeler, The Cut, "When Will We Stop Shaming Ambitious Women?," 5 Jan. 2018 No one knows yet if the man has been identified or if his wife has brained him with a skillet or filed for divorce. Ellie Delano, Woman's Day, "In The Age Of Social Media And Smartphones, No Cheater Is Safe," 11 June 2013

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'brain.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

See More

First Known Use of brain

Noun

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

Verb

14th century, in the meaning defined at sense 1

History and Etymology for brain

Noun

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

Keep scrolling for more

Learn More about brain

Statistics for brain

Last Updated

5 Oct 2018

Look-up Popularity

Time Traveler for brain

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

See more words from the same century

Keep scrolling for more

More Definitions for brain

brain

noun

English Language Learners Definition of brain

 (Entry 1 of 2)

: the organ of the body in the head that controls functions, movements, sensations, and thoughts

: the ability to think and reason

: a very intelligent person

brain

verb

English Language Learners Definition of brain (Entry 2 of 2)

: to hit (someone) on the head very hard

brain

noun
\ˈbrān \

Kids Definition of brain

 (Entry 1 of 2)

1 : the part of the nervous system that is inside the skull, consists of grayish nerve cells and whitish nerve fibers, and is the organ of thought and the central control point for the nervous system

2 : the ability to think : intelligence

3 : someone who is very smart

brain

verb
brained; braining

Kids Definition of brain (Entry 2 of 2)

: to hit on the head very hard

brain

noun
\ˈbrān \

Medical Definition of brain 

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

Keep scrolling for more

Comments on brain

What made you want to look up brain? Please tell us where you read or heard it (including the quote, if possible).

WORD OF THE DAY

not any or not one

Get Word of the Day daily email!

Test Your Vocabulary

Great Scrabble Words—A Quiz

  • scrabble-tiles-that-read-scrabble-quiz
  • Which of the following Q-without-U words means the number five in cards or dice?
Spell It

Can you spell these 10 commonly misspelled words?

TAKE THE QUIZ
SCRABBLE® Sprint

Test Your Knowledge - and learn some interesting things along the way.

TAKE THE QUIZ

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!