crackbrain

1 a person judged to be legally or medically insane once a brilliant dancer, he died a crackbrain in a mental institution Synonyms bug, lunatic, crazy, fool, fruitcake, head case, loon, loony, maniac, nut, nutcase, nutter [British slang], psycho, psychopath, sickie, sicko, wacko (also whacko)Related Words madman, madwoman; abnormal, deviant; manic-depressive, monomaniac, mythomaniac, neurotic, obsessive, obsessive-compulsive, paranoid, psychoneurotic, psychotic, schizo, schizoid, schizophrene, schizophrenic, sociopath; character, codger, crack, crackpot, crank, eccentric, fantastic (also fantastical), flake, kook, oddball, oddity, original, quiz, screwball, tyke (also tike) [chiefly British], weirdo, zany; case, patient

2 a person of odd or whimsical habits a crackbrain who wore bedroom slippers to the grocery shop Synonyms character, codger, crack, eccentric, crackpot, crank, flake, fruitcake, head case, kook, nut, nutcase, nutter [British slang], oddball, oddity, original, quiz, screwball, weirdo, zanyRelated Words bohemian, maverick, nonconformist, quixote; coot, geezer; curio, rarity; freak; fantast, fantasticoNear Antonyms conformer, conformist, follower, sheep