Definition of "Gun" :

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

"Two runners started before the gun."

noun: a pedal that controls the throttle valve

noun: large but transportable armament

noun: a hand-operated pump that resembles a pistol; forces grease into parts of a machine

noun: a weapon that discharges a missile at high velocity (especially from a metal tube or barrel)

noun: a professional killer who uses a gun

noun: a person who shoots a gun (as regards their ability)

verb: shoot with a gun