From WordNet (r) 3.0 (2006) [wn]:
shotgun
n 1: firearm that is a double-barreled smoothbore shoulder
weapon for firing shot at short ranges [syn: shotgun,
scattergun]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Shotgun \Shot"gun`\, n.
A light, smooth-bored gun, often double-barreled, especially
designed for firing small shot at short range, and killing
small game.
[1913 Webster]