[1] : WordNet (r) 2.0

knucklehead
     n : these words are used to express a low opinion of someone's
         intelligence syn: dunce, dunderhead, numskull, blockhead,
          bonehead, lunkhead, hammerhead, loggerhead, muttonhead,
          shithead, fuckhead
see also:
dunce dunderhead numskull blockhead bonehead lunkhead 
hammerhead loggerhead muttonhead shithead fuckhead 

[2] : Moby Thesaurus II by Grady Ward, 1.0

40 moby thesaurus words for "knucklehead":
   addlebrain, addlehead, addlepate, beefhead, blockhead, blubberhead,
   blunderhead, bonehead, bufflehead, cabbagehead, chowderhead,
   chucklehead, clodhead, clodpate, clodpoll, dolthead, dullhead,
   dumbhead, dunderhead, dunderpate, fathead, jolterhead, jughead,
   lunkhead, meathead, muddlehead, mushhead, muttonhead, noodlehead,
   numskull, peabrain, pinbrain, pinhead, puddinghead, pumpkin head,
   puzzlehead, stupidhead, thickhead, thickskull, tottyhead

Knucklehead >> K Words
Knucklehead, definition of term: Knucklehead
knucklehead_pag1.html