brain, encephalon -- (that part of the central nervous system that includes all the higher nervous centers; enclosed within the skull; continuous with the spinal cord)
mind, head, brain, psyche, nous -- (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")
genius, mastermind, brain, brainiac, Einstein -- (someone who has exceptional intellectual ability and originality; "Mozart was a child genius"; "he's smart but he's no Einstein")
brain -- (the brain of certain animals used as meat)