river vs River Trent

river and River Trent both are nouns.

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

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