Source : Webster's Revised Unabridged Dictionary (1913)

Blunderbuss \Blun"der*buss\, n. [Either fr. blunder + D. bus
   tube, box, akin to G. b["u]chse box, gun, E. box; or
   corrupted fr. D. donderbus (literally) thunder box, gun,
   musket.]
   1. A short gun or firearm, with a large bore, capable of
      holding a number of balls, and intended to do execution
      without exact aim.

   2. A stupid, blundering fellow.

Source : WordNet®

blunderbuss
     n : a short musket of wide bore with a flared muzzle