horse pistol vs pistol

horse pistol and pistol both are nouns.

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

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

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

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

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