canister vs ammo

canister and ammo both are nouns.

Word	Noun	Adjective	Verb	Adverb
canister	Yes	No	No	No
ammo	Yes	No	No	No

As nouns, ammo is a hypernym of canister; that is, ammo is a word with a broader meaning than canister:

canister: a metallic cylinder packed with shot and used as ammunition in a firearm
ammo: projectiles to be fired from a gun

Other hypernyms of canister include ammunition.

canister (noun)	ammo (noun)
metal container for storing dry foods such as tea or flour	projectiles to be fired from a gun
a metallic cylinder packed with shot and used as ammunition in a firearm