horse-pistol vs handgun

horse-pistol and handgun both are nouns.

Word	Noun	Adjective	Verb	Adverb
horse-pistol	Yes	No	No	No
handgun	Yes	No	No	No

As nouns, handgun is a hypernym of horse-pistol; that is, handgun is a word with a broader meaning than horse-pistol:

horse-pistol: a large pistol (usually in a holster) formerly carried by horsemen
handgun: a firearm that is held and fired with one hand

Other hypernyms of horse-pistol include pistol, shooting iron, side arm.

horse-pistol (noun)	handgun (noun)
a large pistol (usually in a holster) formerly carried by horsemen	a firearm that is held and fired with one hand