river vs Red River of the South

river and Red River of the South both are nouns.

Word	Noun	Adjective	Verb	Adverb
river	Yes	No	No	No
Red River of the South	Yes	No	No	No

river (noun)	Red River of the South (noun)
a large natural stream of water (larger than a creek)	a tributary of the Mississippi River that flows eastward from Texas along the southern boundary of Oklahoma and through Louisiana