region vs domain

region and domain both are nouns.

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

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

region: a knowledge domain that you are interested in or are communicating about
domain: the content of a particular field of knowledge

Other hypernyms of region include knowledge base, knowledge domain.

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

region (noun)	domain (noun)
a part of an animal that has a special function or is supplied by a given artery or nerve	the content of a particular field of knowledge
a knowledge domain that you are interested in or are communicating about	people in general; especially a distinctive group of people with some shared interest
the extended spatial location of something	(mathematics) the set of values of the independent variable for which a function is defined
a large indefinite location on the surface of the Earth	territory over which rule or control is exercised
the approximate amount of something (usually used prepositionally as in `in the region of')	a particular environment or walk of life