E layer vs region

E layer and region both are nouns.

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

E 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')