Caucasus vs chain of mountains

Caucasus and chain of mountains both are nouns.

Word	Noun	Adjective	Verb	Adverb
Caucasus	Yes	No	No	No
chain of mountains	Yes	No	No	No

Caucasus (noun)	chain of mountains (noun)
a large region between the Black and Caspian seas that contains the Caucasus Mountains; oil is its major resource	a series of hills or mountains
the mountain range in Caucasia between the Black Sea and the Caspian Sea that forms part of the traditional border between Europe and Asia