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
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
(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
brained; braining; brains
Synonyms
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
Melissa Ruggieri, USA TODAY, 2 Feb. 2025
The Two Point games are perfect for newcomers to the genre, offering just enough challenge and plenty of whimsical scenarios to get your brain jogging.
—David Faris, Newsweek, 2 Feb. 2025
Michael Franco, New Atlas, 29 Dec. 2024
Ode to Lucy’s Pelvis Adrienne Gruber O wondrous one, your bipedal swag, terrestrial locomotion,
partial appendages revealed, brain a soft sponge, size
of an acorn, still waiting for that growth spurt
3.2 million years later.
—Max Ufberg, hazlitt.net, 10 Jan. 2025
See all Example Sentences for brain 
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Opinions expressed in the examples do not represent those of Merriam-Webster or its editors.
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Noun
Davis was responsible for brokering the friendship between Mitchell and Brandi Carlile, who was instrumental in urging Mitchell to return to music following a debilitating brain aneurysm in 2015.
—Melissa Ruggieri, USA TODAY, 2 Feb. 2025
The Two Point games are perfect for newcomers to the genre, offering just enough challenge and plenty of whimsical scenarios to get your brain jogging.
—David Faris, Newsweek, 2 Feb. 2025
Verb
As anyone who's ever seen a mouse navigate a maze knows, the animals are often used in studies to understand the way in which brains function.
—Michael Franco, New Atlas, 29 Dec. 2024
Ode to Lucy’s Pelvis Adrienne Gruber O wondrous one, your bipedal swag, terrestrial locomotion,
partial appendages revealed, brain a soft sponge, size
of an acorn, still waiting for that growth spurt
3.2 million years later.
—Max Ufberg, hazlitt.net, 10 Jan. 2025
See all Example Sentences for brain
Articles Related to brain
Dictionary Entries Near brain
Cite this Entry
“Brain.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/brain. Accessed 6 Feb. 2025.
Copy CitationKids Definition
brain
1 of 2 noun1
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 verb1
: to kill by smashing the skull
2
: to hit on the head
Medical Definition
brain
noun1
: 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
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