gun vs heavy weapon

gun and heavy weapon both are nouns.

Word	Noun	Adjective	Verb	Adverb
gun	Yes	No	Yes	No
heavy weapon	Yes	No	No	No

As nouns, gun and heavy weapon are synonyms defined as:

Other synonyms of gun include artillery, ordnance.

gun (noun)	heavy weapon (noun)
the discharge of a firearm as signal or as a salute in military ceremonies	large but transportable armament
a weapon that discharges a missile at high velocity (especially from a metal tube or barrel)
large but transportable armament
a hand-operated pump that resembles a pistol; forces grease into parts of a machine
a pedal that controls the throttle valve
a professional killer who uses a gun
a person who shoots a gun (as regards their ability)

gun (verb)	heavy weapon (verb)
shoot with a gun