Caucasus vs Caucasia

Caucasus and Caucasia both are nouns.

Word	Noun	Adjective	Verb	Adverb
Caucasus	Yes	No	No	No
Caucasia	Yes	No	No	No

As nouns, Caucasus and Caucasia are synonyms defined as:

Caucasus and Caucasia: a large region between the Black and Caspian seas that contains the Caucasus Mountains; oil is its major resource

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