shotgun vs firearm

shotgun and firearm both are nouns.

Word	Noun	Adjective	Verb	Adverb
shotgun	Yes	No	No	No
firearm	Yes	No	No	No

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

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

Other hypernyms of shotgun include piece, small-arm.

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