U.S. vs Niagara River

U.S. and Niagara River both are nouns.

Word	Noun	Adjective	Verb	Adverb
U.S.	Yes	No	No	No
Niagara River	Yes	No	No	No

U.S. (noun)	Niagara River (noun)
the executive and legislative and judicial branches of the federal government of the United States	a river flowing from Lake Erie into Lake Ontario; forms boundary between Ontario and New York
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