scattergun vs small-arm

scattergun and small-arm both are nouns.

Word	Noun	Adjective	Verb	Adverb
scattergun	Yes	No	No	No
small-arm	Yes	No	No	No

As nouns, small-arm is a hypernym of scattergun; that is, small-arm is a word with a broader meaning than scattergun:

scattergun: firearm that is a double-barreled smoothbore shoulder weapon for firing shot at short ranges
small-arm: a portable gun

Other hypernyms of scattergun include firearm, piece.

scattergun (noun)	small-arm (noun)
firearm that is a double-barreled smoothbore shoulder weapon for firing shot at short ranges	a portable gun