The Collaborative International Dictionary of English v.0.48:

Blockish \Block"ish\, a.
   Like a block; deficient in understanding; stupid; dull.
   "Blockish Ajax." --Shak. -- Block"ish*ly, adv. --
   Block"ish*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

blockish
    adj 1: resembling a block in shape [syn: blockish, blocky]

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "blockish":
   Boeotian, asinine, beef-brained, beef-witted, blockheaded, bovine,
   chuckleheaded, chumpish, cloddish, cowish, crass, dense, doltish,
   dull, dullard, dumb, duncical, duncish, fat, gross, ineducable,
   klutzy, lumpish, numskulled, oafish, opaque, sottish, stupid,
   thick, unteachable, wrongheaded