Дурак (дура), дуралей, дурачок, дурень, дурачина, болван, бревно, дерево, дубина, идиот, пень, телепень, глупец, глупыш, глупенький, балбес, оболтус, олух, осел, остолоп, простофиля, фалалей, фофан.
(= 24 синонима)
[Абрамов Н. Словарь русских синонимов и сходных по смыслу выражений]
Fool, airhead, birdbrain, blockhead, bonehead, bubblehead, chowderhead, chucklehead, clodpoll (or clodpole), clot, cluck, clunk, cretin, cuddy (or cuddie), deadhead, dimwit, dip, dodo, dolt, donkey, doofus, dope, dullard, dumbbell, dumbhead, dum-dum, dummkopf, dummy, dunce, dunderhead, idiot, fathead, gander, golem, goof, goon, half-wit, hammerhead, hardhead, ignoramus, imbecile, jackass, know-nothing, knucklehead, lamebrain, loggerhead, loon, lump, lunkhead, meathead, mome, moron, mug, mutt, natural, nincompoop, ninny, nin-nyhammer, nit, nitwit, noddy, noodle, numskull (or numbskull), oaf, pinhead, prat, saphead, shlub, simpleton, stock, stupe, stupid, thickhead, turkey, woodenhead, yahoo, yo-yo.
(= 83 синонима)
[Merriam-Webster Dictionary]