a.
Dull, stupid, obtuse, foolish, senseless, witless, insensible, sluggish, stolid, mindless, brainless, weak-headed, addle-headed, addle-pated, blunder-headed, muddle-headed, beef-witted, bovine, fat-headed, dull-brained, shallow-brained, lack-witted, short-witted, dull-witted, blunt-witted, shallow-pated, clod-pated, thick-skulled, wanting, heavy, doltish, sottish, blockish, wooden-headed, dunderheaded, bull-headed, slow, slow of apprehension, void of understanding.