outback vs bush

outback and bush both are nouns.

Word	Noun	Adjective	Verb	Adverb
outback	Yes	Yes	No	No
bush	Yes	Yes	Yes	No

As nouns, bush is a hypernym of outback; that is, bush is a word with a broader meaning than outback:

outback (noun)	bush (noun)
the bush country of the interior of Australia	hair growing in the pubic area
	dense vegetation consisting of stunted trees or bushes
	a large wilderness area
	a low woody perennial plant usually having several major stems

outback (adjective)	bush (adjective)
inaccessible and sparsely populated	not of the highest quality or sophistication

outback (verb)	bush (verb)
	provide with a bushing