American vs United States of America

American and United States of America both are nouns.

Word	Noun	Adjective	Verb	Adverb
American	Yes	Yes	No	No
United States of America	Yes	No	No	No

American (noun)	United States of America (noun)
the English language as used in the United States	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
a native or inhabitant of the United States
a native or inhabitant of a North American or Central American or South American country

American (adjective)	United States of America (adjective)
of or relating to or characteristic of the continents and islands of the Americas
of or relating to the United States of America or its people or language or culture