river vs River Ouse

river and River Ouse both are nouns.

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

river (noun)	River Ouse (noun)
a large natural stream of water (larger than a creek)	a river in northeastern England that flows generally southeastward to join the Trent River and form the Humber