nincompoop

noun

don't be such a nincompoop:

idiot, fool, halfwit, dunce, dolt, ignoramus, cretin, imbecile, dullard, moron, simpleton, clod;

informal dope, ninny, chump, dimwit, nitwit, goon, dumbo, dum-dum, dummy, dumb-bell, loon, jackass, bonehead, fathead, numbskull, blockhead, dunderhead, chucklehead, knucklehead, muttonhead, pudding-head, thickhead, wooden-head, airhead, pinhead, lamebrain, pea-brain, birdbrain, zombie, jerk, nerd, dipstick, donkey, noodle;

British, informal nit, twit, numpty, clot, ass, plonker, berk, prat, pillock, wally, git, wazzock, divvy, nerk, twerp, twonk, charlie, mug, muppet;

Scottish, informal nyaff, balloon, sumph, gowk;

Irish, informal gobdaw;

North American, informal schmuck, bozo, boob, lamer, turkey, schlepper, chowderhead, dumbhead, dumbass, goofball, goof, goofus, galoot, dork, lummox, klutz, putz, schlemiel, sap, gink, cluck, clunk, ding-dong, dingbat, wiener, weeny, dip, simp, spud, coot, palooka, poop, squarehead, yo-yo, dingleberry;

US, informal wing nut;

Australian, New Zealand, informal drongo, dill, alec, galah, nong, bogan, poon, boofhead;

South African, informal mompara;

British, vulgar slang arse, arsehole, knobhead, twat, wanker;

North American, vulgar slang ass, asshole, asshat;

archaic tomfool, noddy, clodpole, loggerhead, spoony, mooncalf.

nincompoop Oxford Dictionary of English