Caspian Sea vs Caspian

Caspian Sea and Caspian both are nouns.

Word	Noun	Adjective	Verb	Adverb
Caspian Sea	Yes	No	No	No
Caspian	Yes	No	No	No

As nouns, Caspian Sea and Caspian are synonyms defined as:

Caspian Sea and Caspian: a large saltwater lake between Iran and Russia fed by the Volga River; the largest inland body of water in the world

Caspian Sea (noun)	Caspian (noun)
a large saltwater lake between Iran and Russia fed by the Volga River; the largest inland body of water in the world	a large saltwater lake between Iran and Russia fed by the Volga River; the largest inland body of water in the world