region vs dominion

region and dominion both are nouns.

Word	Noun	Adjective	Verb	Adverb
region	Yes	No	No	No
dominion	Yes	No	No	No

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

region (noun)	dominion (noun)
a part of an animal that has a special function or is supplied by a given artery or nerve	a region marked off for administrative or other purposes
a knowledge domain that you are interested in or are communicating about	dominance or power through legal authority
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')