Mississippi River vs United States of America

Mississippi River and United States of America both are nouns.

Word	Noun	Adjective	Verb	Adverb
Mississippi River	Yes	No	No	No
United States of America	Yes	No	No	No

Mississippi River (noun)	United States of America (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	North American republic containing 50 states - 48 conterminous states in North America plus Alaska in northwest North America and the Hawaiian Islands in the Pacific Ocean; achieved independence in 1776