critter vs fauna

critter and fauna both are nouns.

Word	Noun	Adjective	Verb	Adverb
critter	Yes	No	No	No
fauna	Yes	No	No	No

As nouns, fauna is a hypernym of critter; that is, fauna is a word with a broader meaning than critter:

Other hypernyms of critter include animal, animate being, beast, brute, creature.

critter (noun)	fauna (noun)
a regional term for `creature' (especially for domestic animals)	a living organism characterized by voluntary movement
	all the animal life in a particular region or period