region vs demesne

region and demesne both are nouns.

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

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

region (noun)	demesne (noun)
a part of an animal that has a special function or is supplied by a given artery or nerve	territory over which rule or control is exercised
a knowledge domain that you are interested in or are communicating about	extensive landed property (especially in the country) retained by the owner for his own use
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')