dumbbell (n.)

ass, blockhead, bonehead, boob, booby, chump, cretin, dimwit, dolt, dope, dumbo, dummy, dunce, fathead, hammerhead, idiot, loggerhead, moron, nincompoop, nitwit, numskull, nut, peabrain, pinhead

dumbbell (n.) (colloquial)

ass, bonehead, changeling, chump, cretin, dimwit, dolt, donkey, dope, dumbo, dummy, dunce, fathead, fool, half-wit, idiot, imbecile, moron, nincompoop, nitwit, numskull, nut, oaf, retard, berk (British), booby (informal), bugger (colloquial, spéc. anglais britannique), burk (British), damn fool (colloquial), hammerhead (American), jackass (colloquial, U.S.A.), loggerhead (old), peabrain (colloquial), pinhead (informal), twerp (informal), wally (colloquial)