brain

(noun) that part of the central nervous system that includes all the higher nervous centers; enclosed within the skull; continuous with the spinal cord. Synonyms: encephalon.

(noun) mental ability. Synonyms: brainpower, learning ability, mental capacity, mentality, wit. Example: "He's got plenty of brains but no common sense."

(noun) that which is responsible for one's thoughts and feelings; the seat of the faculty of reason. Synonyms: mind, head, psyche, nous. Examples: "His mind wandered." "I couldn't get his words out of my head."

(noun) someone who has exceptional intellectual ability and originality. Synonyms: genius, mastermind, brainiac, Einstein. Examples: "Mozart was a child genius." "He's smart but he's no einstein."

(noun) the brain of certain animals used as meat.

(verb) hit on the head.

(verb) kill by smashing someone's skull.