interstellar space vs region

interstellar space and region both are nouns.

Word	Noun	Adjective	Verb	Adverb
interstellar space	Yes	No	No	No
region	Yes	No	No	No

As nouns, region is a hypernym of interstellar space; that is, region is a word with a broader meaning than interstellar space:

Other hypernyms of interstellar space include part.

interstellar space (noun)	region (noun)
the space between stars	a part of an animal that has a special function or is supplied by a given artery or nerve
	a knowledge domain that you are interested in or are communicating about
	the extended spatial location of something
	a large indefinite location on the surface of the Earth
	the approximate amount of something (usually used prepositionally as in `in the region of')