Source : Webster's Revised Unabridged Dictionary (1913)

Blockheaded \Block"head`ed\, a.
   Stupid; dull.

Source : WordNet®

blockheaded
     adj : used informally [syn: {boneheaded}, {fatheaded}, {loggerheaded},
            {thick}, {thickheaded}, {thick-skulled}, {wooden-headed}]