brain
Americannoun
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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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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:
As well as causing seizures, the abnormality was also close to areas of the brain controlling speech, movement and vision.
From BBC ● Jul. 23, 2026
“Measles spreads easily and can lead to serious complications, including pneumonia, brain swelling, and even death.”
From Los Angeles Times ● Jul. 23, 2026
A satisfying puzzle break: What’s a four-letter word for “Those who often hear a siren song”? Treat your brain to some delightful wordplay in today’s crossword.
From Slate ● Jul. 22, 2026
“When you’re going after a mile world record, and you go deep into your brain, that’s when you’re asked the hardest-hitting questions of: Are you capable? Have you done enough?” he said.
From The Wall Street Journal ● Jul. 22, 2026
Phineas's seizures are probably caused by slow changes in brain tissue damaged in the original accident.
From "Phineas Gage" by John Fleischman
Among the waste products the system clears are proteins called amyloid and tau, the deposits that accumulate in the brains of people with Alzheimer's disease.
From BBC ● Jul. 19, 2026
The researchers suggest that larger brains may have provided major evolutionary advantages, even if the hormonal conditions associated with that development also carried biological costs for males.
From Science Daily ● Jul. 17, 2026
The explosion in resource-hungry data centres -- housing the hardware "brains" of artificial intelligence -- is fuelling unease worldwide, with New York State and Australia the latest jurisdictions to announce new rules.
From Barron's ● Jul. 17, 2026
But the genre also requires action, adventure, enlightenment, struggle, the guest-host relationship observed by the ancients and the supremacy of brains over brawn.
From The Wall Street Journal ● Jul. 16, 2026
This poor record of achievement has led scholars to speculate that the internal structure of the brains of these Sapiens was probably different from ours.
From "Sapiens: A Brief History of Humankind" by Yuval Noah Harari
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 Reid, Mayne
"And for well-nigh braining an officer of his Majesty's infantry!" said old Major Elliott, putting his head over the hedge.
From The Great Shadow and Other Napoleonic Tales by Doyle, Arthur Conan, Sir
The second was a deep gully, but so choked with rubble that after nearly braining myself I desisted.
From Prester John by Buchan, John
Oh the demons, they were cackling while he sat devouring a great moose joint, until he was close to braining them with the yellow ball of the joint.
From The Best Short Stories of 1917 and the Yearbook of the American Short Story by O'Brien, Edward J. (Edward Joseph Harrington)
Definitions 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.
