river vs Potomac River

river and Potomac River both are nouns.

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

river (noun)	Potomac River (noun)
a large natural stream of water (larger than a creek)	a river in the east central United States; rises in West Virginia in the Appalachian Mountains and flows eastward, forming the boundary between Maryland and Virginia, to the Chesapeake Bay