Bighorn River vs Bighorn

Bighorn River and Bighorn both are nouns.

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

As nouns, Bighorn River and Bighorn are synonyms defined as:

Bighorn River and Bighorn: a river that flows from central Wyoming to the Yellowstone River in southern Montana

Bighorn River (noun)	Bighorn (noun)
a river that flows from central Wyoming to the Yellowstone River in southern Montana	a river that flows from central Wyoming to the Yellowstone River in southern Montana