The Collaborative International Dictionary of English v.0.48:

Blunderhead \Blun"der*head`\, n. [Blunder + head.]
   A stupid, blundering fellow.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

63 Moby Thesaurus words for "blunderhead":
   addlebrain, addlehead, addlepate, beefhead, blockhead, blubberhead,
   blunderer, bonehead, boor, botcher, bufflehead, bumbler, bungler,
   cabbagehead, chowderhead, chucklehead, clod, clodhead, clodhopper,
   clodknocker, clodpate, clodpoll, clot, clown, dolt, dolthead,
   dullhead, dumbhead, dunderhead, dunderpate, fathead, fumbler, gawk,
   gowk, jolterhead, jughead, klutz, knucklehead, looby, lout, lubber,
   lunkhead, meathead, muddlehead, mushhead, muttonhead, noodlehead,
   numskull, oaf, ox, peabrain, pinbrain, pinhead, puddinghead,
   pumpkin head, puzzlehead, slouch, slubberer, stupidhead, thickhead,
   thickskull, tottyhead, yokel