river vs Uruguay River

river and Uruguay River both are nouns.

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

river (noun)	Uruguay River (noun)
a large natural stream of water (larger than a creek)	a South American river that arises in southern Brazil and flows south to the Rio de la Plata; the northern section forms the boundary between Argentina and Brazil and the southern section forms the boundary between Argentina and Uruguay