brain
Americannoun
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brains
plural
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Anatomy, Zoology. the part of the central nervous system enclosed in the cranium of humans and other vertebrates, consisting of a soft, convoluted mass of gray and white matter and serving to control and coordinate the mental and physical actions.
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Zoology. (in many invertebrates) a part of the nervous system more or less corresponding to the brain of vertebrates.
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(used with a plural verb) Sometimes brains. understanding; intellectual power; intelligence.
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the brain as the center of thought, understanding, etc.; mind; intellect.
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Slang. brains, a member of a group who is regarded as its intellectual leader or planner.
The junior partner is the brains of the firm.
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Informal. a very intelligent or brilliant person.
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Informal.
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the controlling or guiding mechanism in a computer, robot, pacemaker, etc.
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the part of a computer system for coordination or guidance, as of a missile.
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verb (used with object)
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brains,
present (3rd person singular)
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brained,
past participle, past
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braining
present participle
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to smash the skull of.
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Slang. to hit or bang (someone) on the head.
idioms
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beat one's brains out, to try very hard to understand and work out a problem, remember something, etc..
She beat her brains out studying for the exam.
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have something on the brain, to have an obsession; be occupied with.
Lately I seem to have food on the brain.
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pick someone's brains, to obtain information by questioning another person rather than by seeking it independently.
He refused to prepare for the exam but counted on being able to pick his roommate's brains.
noun
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Technical name: encephalon. the soft convoluted mass of nervous tissue within the skull of vertebrates that is the controlling and coordinating centre of the nervous system and the seat of thought, memory, and emotion. It includes the cerebrum, brainstem, and cerebellum
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the main neural bundle or ganglion of certain invertebrates
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informal (often plural) intellectual ability
he's got brains
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informal shrewdness or cunning
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informal an intellectual or intelligent person
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informal (usually plural; functioning as singular) a person who plans and organizes an undertaking or is in overall control of an organization, etc
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an electronic device, such as a computer, that performs apparently similar functions to the human brain
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constantly in mind
I had that song on the brain
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to obtain information or ideas from someone
verb
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to smash the skull of
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slang to hit hard on the head
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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.
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See more at brainstem cerebellum cerebrum
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A bundle of nerves in many invertebrate animals that is similar to the vertebrate brain in function and position.
Usage
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.
Synonym Usage
See mind.
Other Word Forms
Derived Forms
Inflected Forms
Nouns
Participles
Conjugated Forms
Present
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brainsimple
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brainssimple
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have brainedperfect
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has brainedperfect
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am brainingprogressive
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are brainingprogressive
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is brainingprogressive
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have been brainingperfect progressive
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has been brainingperfect progressive
Past
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brainedsimple
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had brainedperfect
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was brainingprogressive
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were brainingprogressive
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had been brainingperfect progressive
Future
Etymology
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 ( def. )
Explanation
The brain is the most complex organ in the body, located inside the protective skull. The word can also be used as a verb in the phrase "to brain," which means to injure or kill someone by hitting them in the head. The human brain has inspired many idioms, or colorful phrases. Thinking intently (or obsessively) about something means that you've got it "on the brain," and to "pick someone's brain" means to get their ideas on something. A puzzle is a "brainteaser, someone smart is called "a brain," and the person who runs something is said to be "the brains" of the operation.
Vocabulary lists containing brain
Common Five-letter Words for Wordle, List 3
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Human Anatomy and Physiology - Introductory
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Human Anatomy and Physiology - High School
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
See Examples For:
Layer 5 pyramidal neurons serve as important communication pathways that send information from the cortex to other brain regions.
From Science Daily ● Nov. 7, 2026
Changes in their number, strength, and organization can alter the way information travels through the brain.
From Science Daily ● Nov. 7, 2026
Additional research will be necessary to determine whether the same cellular mechanisms operate in humans and whether separating brain rewiring from psychedelic effects can produce effective treatments for depression, PTSD, or other psychiatric disorders.
From Science Daily ● Nov. 7, 2026
In other words, the cellular pathway responsible for psilocybin's brain rewiring can be separated from the pathway responsible for this particular behavioral marker of psychedelic activity.
From Science Daily ● Nov. 7, 2026
Their brain injuries usually follow surgery to remove a tumor from deep inside the frontal cortex.
From "Phineas Gage" by John Fleischman
Excessive caffeine consumption has been linked to headaches and sleep problems, and experts say young people can be more sensitive to caffeine as they have smaller bodies and their brains are still developing.
From BBC ● Nov. 6, 2026
Earlier research found that disruptions in this pathway were associated with the formation of amyloid-beta deposits in the brains of rats.
From Science Daily ● Nov. 3, 2026
“I think this helps us recalibrate our brains ... to connect with others and take notice of what’s going on around us.”
From Los Angeles Times ● Nov. 3, 2026
The situation hasn’t changed with the dismissal of head coach John Harbaugh and the arrival of Minter and a whole new set of sideline brains.
From The Wall Street Journal ● Nov. 2, 2026
It is true that ostriches have exceedingly tiny brains relative to their size, yet even ostriches are not quite as dim-witted as all that.
From "The Unseen Guest" by Maryrose Wood
They found that the larger brained primate species did not solve the fruit-finding puzzle more efficiently than smaller brained mammals.
From Science Daily ● May 28, 2024
Clevinger, his long hair brained into pigtails, allowed three runs, two earned, and six hits in 4 1/3 innings while striking out six and walking two.
From Seattle Times ● May 10, 2022
At least there’s nothing pointy on the Steam Deck, unlike some of the book corners I’ve brained myself with over the years.
From The Verge ● Mar. 29, 2022
A second major find, the nearly complete skull of a larger brained hominid, long known simply by its field number “1470” and now classified as H. rudolfensis, bolstered that point.
From Science Magazine ● Jan. 2, 2022
Raizel and I scooted out of the way to avoid being brained by one.
From "The City Beautiful" by Aden Polydoros
We are a long way here from Thor developing the wheel or the Fat Broad braining the Snake.
From Time Magazine Archive
They succeed; but not without difficulty, and a free handling of handspikes—almost braining the apes before they consent to relinquish it.
From The Flag of Distress A Story of the South Sea by Mayne Reid
Early after breakfast on that morning,—that morning on which Tappitt had for a moment thought of braining Luke Rowan with the poker,—Mrs. Ray started from the cottage on her mission into Baslehurst.
From Rachel Ray by Anthony Trollope
Both men ducked instinctively, to escape a braining.
From The Black Bag by Louis Joseph Vance
"Théo is at home—he went to tell his mother," Joyselle said, nearly braining an old lady with his violin-case as he swung round to speak.
From The Halo by B. Martin Justice
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Get a wordDefinitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
