Mississippi vs Southern United States

Mississippi and Southern United States both are nouns.

Word	Noun	Adjective	Verb	Adverb
Mississippi	Yes	No	No	No
Southern United States	Yes	No	No	No

Mississippi (noun)	Southern United States (noun)
a state in the Deep South on the gulf of Mexico; one of the Confederate States during the American Civil War	the region of the United States lying to the south of the Mason-Dixon line
a major North American river and the chief river of the United States; rises in northern Minnesota and flows southward into the Gulf of Mexico