river vs Arno River

river and Arno River both are nouns.

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

river (noun)	Arno River (noun)
a large natural stream of water (larger than a creek)	a river in central Italy rising in the Apennines and flowing through Florence and Pisa to the Ligurian Sea