animal group vs litter

animal group and litter both are nouns.

Word	Noun	Adjective	Verb	Adverb
animal group	Yes	No	No	No
litter	Yes	No	Yes	No

As nouns, litter is a hyponym of animal group; that is, litter is a word with a more specific, narrower meaning than animal group:

Other hyponyms of animal group include team, brood, flock, flock, fold, herd, herd, pack, pod, pride, clowder, school, shoal, caste, colony, warren, breed, stock, strain, drove.

animal group (noun)	litter (noun)
a group of animals	material used to provide a bed for animals
	conveyance consisting of a chair or bed carried on two poles by bearers
	the offspring at one birth of a multiparous mammal
	rubbish carelessly dropped or left about (especially in public places)

animal group (verb)	litter (verb)
	give birth to a litter of animals
	make a place messy by strewing garbage around
	strew