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
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
Megan Feringa, New York Times, 27 June 2025
Some researchers have reported that ibogaine may be able to help repair areas of the brain by increasing levels of molecules called trophic factors that encourage brain cells to foster new connections, said Kratter, the Stanford researcher.
—Clara Harter, Los Angeles Times, 26 June 2025
Ajdina Halilovic, Quanta Magazine, 7 May 2025
Just before Louise gets kidnapped off the street, Joe — who was, conveniently, stalking her at the time — swoops in to brain that dude with a brick.
—Jessica M. Goldstein, Vulture, 25 Apr. 2025
See All Example Sentences for brain
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Noun
Everton midfielder Hayley Ladd is the brains of the operation now, while Liverpool counterpart Ceri Holland has become a reliable source of goals and energy.
—Megan Feringa, New York Times, 27 June 2025
Some researchers have reported that ibogaine may be able to help repair areas of the brain by increasing levels of molecules called trophic factors that encourage brain cells to foster new connections, said Kratter, the Stanford researcher.
—Clara Harter, Los Angeles Times, 26 June 2025
Verb
Introduction May 7, 2025 biology brains cells memory molecular biology neurons neuroscience proteins All topics
(opens a new tab)
When Todd Sacktor (opens a new tab) was about to turn 3, his 4-year-old sister died of leukemia.
—Ajdina Halilovic, Quanta Magazine, 7 May 2025
Just before Louise gets kidnapped off the street, Joe — who was, conveniently, stalking her at the time — swoops in to brain that dude with a brick.
—Jessica M. Goldstein, Vulture, 25 Apr. 2025
See All Example Sentences for brain
Cite this Entry
“Brain.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/brain. Accessed 3 Jul. 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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