river vs Arkansas River

river and Arkansas River both are nouns.

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

river (noun)	Arkansas River (noun)
a large natural stream of water (larger than a creek)	a river that rises in the Rocky Mountains in Colorado and flows southeast through Kansas and Oklahoma and through Arkansas to become a tributary of the Mississippi River