region vs vacuity

region and vacuity both are nouns.

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

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

region (noun)	vacuity (noun)
a part of an animal that has a special function or is supplied by a given artery or nerve	total lack of meaning or ideas
a knowledge domain that you are interested in or are communicating about	a region that is devoid of matter
the extended spatial location of something	the absence of matter
a large indefinite location on the surface of the Earth
the approximate amount of something (usually used prepositionally as in `in the region of')