Heaviside layer vs region

Heaviside layer and region both are nouns.

Word	Noun	Adjective	Verb	Adverb
Heaviside layer	Yes	No	No	No
region	Yes	No	No	No

Heaviside layer (noun)	region (noun)
a region of the ionosphere (from 50 to 90 miles up) that reflects radio waves of medium length	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')