loon

1 a person judged to be legally or medically insane giggled like a loon at his own jokes Synonyms bug, crackbrain, crazy, fool, fruitcake, head case, lunatic, 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 stupid person the loons at the grocery store had put the potato chips at the bottom of the bag Synonyms airhead, birdbrain, blockhead, bonehead, bubblehead, chowderhead, chucklehead, clodpoll (or clodpole), clot [British], cluck, clunk, cretin, cuddy (or cuddie) [British dialect], deadhead, dim bulb [slang], dimwit, dip, dodo, dolt, donkey, doofus [slang], dope, dork [slang], dullard, dumbbell, dumbhead, dum-dum, dummkopf, dummy, dunce, dunderhead, fathead, gander, golem, goof, goon, half-wit, hammerhead, hardhead, ignoramus, imbecile, jackass, know-nothing, knucklehead, lamebrain, loggerhead [chiefly dialect], idiot, lump, lunkhead, meathead, mome [archaic], moron, mug [chiefly British], mutt, natural, nimrod [slang], nincompoop, ninny, ninnyhammer, nit [chiefly British], nitwit, noddy, noodle, numskull (or numbskull), oaf, pinhead, prat [British], ratbag [chiefly Australian], saphead, schlub (also shlub) [slang], schnook [slang], simpleton, stock, stupe, stupid, thickhead, turkey, woodenhead, yahoo, yo-yoRelated Words booby, buffoon, fool, goose, loony, lunatic, madman, nut, zany; loser; gawk; featherbrain, scatterbrain; beast, boor, cad, churl, clown, creep, cur, heel, jerk, skunk, snake, stinker, villain; bimbette [slang], bimbo [slang], himboNear Antonyms egghead, intellect, intellectual, sage, thinker, whiz, wizard; polymath, Renaissance man; sharpie (or sharpy)Antonyms brain, genius