USA vs Niagara

USA and Niagara both are nouns.

Word	Noun	Adjective	Verb	Adverb
USA	Yes	No	No	No
Niagara	Yes	No	No	No

USA (noun)	Niagara (noun)
the army of the United States of America; the agency that organizes and trains soldiers for land warfare	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	waterfall in Canada is the Horseshoe Falls; in the United States it is the American Falls