brain -
that part of the central nervous system that includes all the higher nervous centers; enclosed within the skull; continuous with the spinal cord
brain-stem,
brain stem,
brainstem the part of the brain continuous with the spinal cord and comprising the medulla oblongata and pons and midbrain and parts of the hypothalamus
brain -
mental ability; "he's got plenty of brains but no common sense"
brain -
that which is responsible for one's thoughts and feelings; the seat of the faculty of reason; "his mind wandered"; "I couldn't get his words out of my head"
The brain is the center of the nervous system in all vertebrate and most invertebrate animals. Some primitive animals such as jellyfish and starfish have a decentralized nervous system without a brain, while sponges lack any nervous system at all. In vertebrates the brain is located in the head, protected by the skull and close to the primary sensory apparatus of vision, hearing, balance, taste, and smell.
OmegaWiki Dictionary
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brain The ability for rational thought.
brain The organ of the central nervous system of an animal located in the skull that controls the actions and thoughts of the animal.
brain An intelligent person.
brain By analogy with a human brain, the part of a machine or computer that performs calculations.
brain The complex of cognitive faculties, mostly characteristic of human beings, that enables consciousness, thinking, reasoning, perception, and judgement.