riot gun vs firearm

riot gun and firearm both are nouns.

Word	Noun	Adjective	Verb	Adverb
riot gun	Yes	No	No	No
firearm	Yes	No	No	No

As nouns, firearm is a hypernym of riot gun; that is, firearm is a word with a broader meaning than riot gun:

riot gun: a firearm designed to disperse rioters rather than to inflict serious injury or death
firearm: a portable gun

Other hypernyms of riot gun include piece, small-arm.

riot gun (noun)	firearm (noun)
a firearm designed to disperse rioters rather than to inflict serious injury or death	a portable gun