American vs United States

American and United States both are nouns.

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

American (noun)	United States (noun)
the English language as used in the United States	the executive and legislative and judicial branches of the federal government of the United States
a native or inhabitant of 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 a North American or Central American or South American country

American (adjective)	United States (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