1. 1. The portion of the vertebrate central nervous system that is enclosed within the cranium, continuous with the spinal cord, and composed of gray matter and white matter. It is the primary center for the regulation and control of bodily activities, receiving and interpreting sensory impulses, and transmitting information to the muscles and body organs. It is also the seat of consciousness, thought, memory, and emotion.
   2. A functionally similar portion of the invertebrate nervous system.
2. 1. Intellectual ability; mind: a dull brain; a quick brain.
   2. Intellectual power; intelligence. Often used in the plural: has brains and good looks. See synonyms at mind.
3. A highly intelligent person.
4. The primary director or planner, as of an organization or movement. Often used in the plural.
5. The control center, as of a ship, aircraft, or spacecraft.

1. To smash in the skull of.
2. To hit on the head.

beat (one's) brains (out)

1. InformalTo exert or expend great mental effort:She beat her brains out during the examination. To exert or expend great mental effort: She beat her brains out during the examination.

1. Obsessively in mind: The coach has winning on the brain.

1. To explore another's ideas through questioning.

1. To think long and hard: I racked my brain for hours trying to recall her name.

[Middle English, from Old English brægen.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.