rubbish vs litter

rubbish and litter both are nouns.

Word	Noun	Adjective	Verb	Adverb
rubbish	Yes	No	Yes	No
litter	Yes	No	Yes	No

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

rubbish: worthless material that is to be disposed of
litter: rubbish carelessly dropped or left about (especially in public places)

Other hyponyms of rubbish include scrap metal, debris, detritus, dust, junk, rubble.

rubbish (noun)	litter (noun)
nonsensical talk or writing	material used to provide a bed for animals
worthless material that is to be disposed of	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)

rubbish (verb)	litter (verb)
attack strongly	give birth to a litter of animals
	make a place messy by strewing garbage around
	strew