region vs Reef

region and Reef both are nouns.

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

region (noun)	Reef (noun)
a part of an animal that has a special function or is supplied by a given artery or nerve	a rocky region in the southern Transvaal in northeastern South Africa; contains rich gold deposits and coal and manganese
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')