Bighorn River vs river

Bighorn River and river both are nouns.

Word	Noun	Adjective	Verb	Adverb
Bighorn River	Yes	No	No	No
river	Yes	No	No	No

Bighorn River (noun)	river (noun)
a river that flows from central Wyoming to the Yellowstone River in southern Montana	a large natural stream of water (larger than a creek)