river vs Penobscot River

river and Penobscot River both are nouns.

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

river (noun)	Penobscot River (noun)
a large natural stream of water (larger than a creek)	a river in central Maine flowing into Penobscot Bay