zip gun vs side arm

zip gun and side arm both are nouns.

Word	Noun	Adjective	Verb	Adverb
zip gun	Yes	No	No	No
side arm	Yes	No	No	No

As nouns, side arm is a hypernym of zip gun; that is, side arm is a word with a broader meaning than zip gun:

Other hypernyms of zip gun include handgun, pistol, shooting iron.

zip gun (noun)	side arm (noun)
a crude homemade pistol	a firearm that is held and fired with one hand