Source : Webster's Revised Unabridged Dictionary (1913)

Lumpish \Lump"ish\, a.
   Like a lump; inert; gross; heavy; dull; spiritless. ``
   Lumpish, heavy, melancholy.'' --Shak. -- {Lump"ish*ly}, adv.
   -- {Lump"ish*ness}, n.

Source : WordNet®

lumpish
     adj : mentally sluggish [syn: {lumpen}, {unthinking}]