Red River of the South vs river

Red River of the South and river both are nouns.

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

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