brain

1 a very smart person the brains all sit together at lunch Synonyms genius, brainiac, intellect, thinker, whiz, wiz, wizardRelated Words polyhistor, polymath, Renaissance man; blue, bluestocking, highbrow, intellectual; sage, savant; egghead, geek, longhair, nerd; master, virtuoso; ace, crackerjack (also crackajack), naturalNear Antonyms ignoramus, illiterate, know-nothing, lowbrow; anti-intellectual, philistine; ass, donkey, fool, jackass; beast, boor, cad, churl, clown, creep, cretin, cur, heel, jerk, louse, lout, skunk, snake, stinkerAntonyms blockhead, dodo, dolt, dope, dumbbell, dummy, dunce, fathead, goon, half-wit, hammerhead, idiot, imbecile, knucklehead, moron, nitwit, numskull (or numbskull), pinhead

2 often brains pl  the ability to learn and understand or to deal with problems you have the brains to figure out that problem on your own Synonyms intelligence(s), brainpower, gray matter, headpiece, intellect, intellectuality, mentality, reason, sense, smartsRelated Words eggheadedness, highbrowism, intellectualism; braininess, brilliance; acumen, alertness, apprehension, astuteness, discernment, discriminability, insight, judgment (or judgement), perception, percipience, perspicacity; common sense, horse sense, mother wit; aptitude, talent; sagacity, sapience, wisdom, wit; head, mind, skullNear Antonyms denseness, density, doltishness, dopiness, dullness (also dulness), dumbness, fatuity, feeblemindedness, foolishness, half-wittedness, idiocy, imbecility, senselessness, simpleness, slowness, stupidity

3 the part of a person that feels, thinks, perceives, wills, and especially reasons I'd love to get inside his brain and experience the world as he experiences it Synonyms mind, cerebrum, head, psyche, thinkerRelated Words belfry, gray matter, intellect, intelligence, loaf [British slang], noodle, reason, skull; acumen, alertness, astuteness, brilliance, insight, judgment (or judgement), mentality, perception, perspicacity, sagacity, sapience, wisdom, wit; awareness, cognizance, consciousness, self-awareness, self-consciousness