Mississippi River vs river

Mississippi River and river both are nouns.

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

Mississippi River (noun)	river (noun)
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	a large natural stream of water (larger than a creek)