river vs Bighorn River

river and Bighorn River both are nouns.

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

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