Definitions of gun:

• noun:   the discharge of a gun as signal or as a salute in military ceremonies

  Example: "A twenty gun salute"

• noun:   a weapon that discharges a missile at high velocity (especially from a metal tube or barrel)
• noun:   a hand-operated pump that resembles a gun; forces grease into parts of a machine
• noun:   a person who shoots a gun (as regards their ability)
• noun:   large but transportable armament
• noun:   a professional killer who uses a gun
• noun:   a pedal that controls the throttle valve
• verb:   shoot with a gun
• name:  A surname (very rare: popularity rank in the U.S.: #84215)