river vs River Severn

river and River Severn both are nouns.

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

river (noun)	River Severn (noun)
a large natural stream of water (larger than a creek)	a river in England and Wales flowing into the Bristol Channel; the longest river in Great Britain