brain

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. 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. n. A functionally similar portion of the invertebrate nervous system.
3. n. Intellectual ability; mind: a dull brain; a quick brain.
4. n. Intellectual power; intelligence. Often used in the plural: has brains and good looks. See Synonyms at mind.
5. n. A highly intelligent person.
6. n. The primary director or planner, as of an organization or movement. Often used in the plural.
7. n. The control center, as of a ship, aircraft, or spacecraft.
8. v. Slang To smash in the skull of.
9. v. Slang To hit on the head.
10. idiom. beat (one's) brains (out) Informal To exert or expend great mental effort: She beat her brains out during the examination.
11. idiom. on the brain Obsessively in mind: The coach has winning on the brain.
12. idiom. brain To explore another's ideas through questioning.
13. idiom. rack (one's) brain Informal To think long and hard: I racked my brain for hours trying to recall her name.

Century Dictionary and Cyclopedia

1. n. In anatomy, the soft grayish and whitish mass filling the cranial cavity of a vertebrate, consisting of ganglionic nerve-cells and nerve-fibers, with the requisite sustentacular and vascular tissue; the encephalon (which see); the part of the cerebrospinal axis which is contained in the cranium. It is divided by anatomists into — the prosencephalon, comprising the cerebral hemispheres (or lateral halves of the cerebrum) with the olfactory lobes;
2. n. In entomology, the principal ganglion of the nervous system, situated in the head, over the esophagus, and formed by the coalescence of serveral supra-esophageal ganglia. The nerves of the eyes and antennæ are directly connected with it, and it gives off two inferior branches which surround the esophagus and unite beneath in the subesophageal ganglion. Sometimes this ganglion is regarded as a part of the brain, being distinguished as the cerebellum, while the principal or upper ganglion is called the cerebrum.
3. n. The same or a corresponding portion of the nervous system in many other invertebrates.
4. n. Understanding; intellectual power; fancy; imagination: commonly in the plural: as, a man of brains; “my brain is too dull,”
5. To dash out the brains of; kill by beating in the skull.
6. Figuratively, to destroy; defeat; balk; thwart.
7. To get into the brain; conceive; understand.

Wiktionary

1. n. The control center of the central nervous system of an animal located in the skull which is responsible for perception, cognition, attention, memory, emotion, and action.
2. n. informal An intelligent person.
3. n. UK, plurale tantum A person who provides the intelligence required for something.
4. n. in the plural Intellect.
5. n. By analogy with a human brain, the part of a machine or computer that performs calculations.
6. v. transitive To dash out the brains of; to kill by smashing the skull.
7. v. transitive, slang To strike (someone) on the head.
8. v. transitive, figuratively To destroy; to put an end to.
9. v. transitive To conceive in the mind; to understand.

GNU Webster's 1913

1. n. (Anat.) The whitish mass of soft matter (the center of the nervous system, and the seat of consciousness and volition) which is inclosed in the cartilaginous or bony cranium of vertebrate animals. It is simply the anterior termination of the spinal cord, and is developed from three embryonic vesicles, whose cavities are connected with the central canal of the cord; the cavities of the vesicles become the central cavities, or ventricles, and the walls thicken unequally and become the three segments, the fore-, mid-, and hind-brain.
2. n. (Zoöl.) The anterior or cephalic ganglion in insects and other invertebrates.
3. n. The organ or seat of intellect; hence, the understanding.
4. n. rare The affections; fancy; imagination.
5. n. informal a very intelligent person.
6. n. informal the controlling electronic mechanism for a robot, guided missile, computer, or other device exhibiting some degree of self-regulation.
7. v. To dash out the brains of; to kill by beating out the brains. To destroy; to put an end to; to defeat.
8. v. obsolete To conceive; to understand.

WordNet 3.0

1. n. that which is responsible for one's thoughts and feelings; the seat of the faculty of reason
2. v. kill by smashing someone's skull
3. n. that part of the central nervous system that includes all the higher nervous centers; enclosed within the skull; continuous with the spinal cord
4. n. someone who has exceptional intellectual ability and originality
5. v. hit on the head
6. n. the brain of certain animals used as meat
7. n. mental ability