nitwit

from WordNet (r) 3.0 (2006)

nitwit
    n 1: a stupid incompetent person [syn: {dimwit}, {nitwit},
         {half-wit}, {doofus}]

from Moby Thesaurus II by Grady Ward, 1.0

32 Moby Thesaurus words for "nitwit":
      Boeotian, block, clod, cluck, dimwit, dolt, donkey, dope, dullard,
      dumb cluck, dumbbell, dummy, dunce, featherweight, gowk,
      jobbernowl, lackwit, lamebrain, lightweight, looby, loon, niais,
      nincompoop, ninny, ninnyhammer, noddy, pinhead, put, simp, stupid,
      thickwit, witling