riot gun vs small-arm

riot gun and small-arm both are nouns.

Word	Noun	Adjective	Verb	Adverb
riot gun	Yes	No	No	No
small-arm	Yes	No	No	No

As nouns, small-arm is a hypernym of riot gun; that is, small-arm 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
small-arm: a portable gun

Other hypernyms of riot gun include firearm, piece.

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