The Collaborative International Dictionary of English v.0.48:

Lummox \Lum"mox\, n.
   A fat, ungainly, stupid person; an awkward bungler. [Low.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

lummox
    n 1: an awkward stupid person [syn: lout, clod,
         stumblebum, goon, oaf, lubber, lummox, lump,
         gawk]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "lummox":
   boor, bumpkin, butterfingers, clod, clodhopper, clumsy, dub,
   duffer, foozler, foul-up, fumble-fist, gawk, gawky, goof, goofball,
   goofer, hayseed, hick, klutz, lobster, looby, lout, lubber, lug,
   lump, muff, muffer, oaf, palooka, rube, slob, stumblebum,
   stumblebunny, yokel