Source : Webster's Revised Unabridged Dictionary (1913)

Smoothbore \Smooth"bore`\, a. (Gun.)
   Having a bore of perfectly smooth surface; -- distinguished
   from rifled. -- n. A smoothbore firearm.

Source : WordNet®

smoothbore
     adj : of a firearm; not having rifling or internal spiral grooves
           inside the barrel [syn: {unrifled}] [ant: {rifled}]