heavy weapon vs cannon

heavy weapon and cannon both are nouns.

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

As nouns, cannon is a hyponym of heavy weapon; that is, cannon is a word with a more specific, narrower meaning than heavy weapon:

Other hyponyms of heavy weapon include field artillery, field gun, four-pounder, depth charge thrower.

heavy weapon (noun)	cannon (noun)
large but transportable armament	a shot in billiards in which the cue ball contacts one object ball and then the other
	lower part of the leg extending from the hock to the fetlock in hoofed mammals
	a large artillery gun that is usually on wheels
	heavy automatic gun fired from an airplane
	(Middle Ages) a cylindrical piece of armor plate to protect the arm
	heavy gun fired from a tank

heavy weapon (verb)	cannon (verb)
	fire a cannon
	make a cannon