OK vs Red River of the South

OK and Red River of the South both are nouns.

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

OK (noun)	Red River of the South (noun)
an endorsement	a tributary of the Mississippi River that flows eastward from Texas along the southern boundary of Oklahoma and through Louisiana
a state in south central United States

OK (adverb)	Red River of the South (adverb)
an expression of agreement normally occurring at the beginning of a sentence