American (n.) Look up American at Dictionary.com
1570s, originally "one of the aboriginal peoples discovered in the Western Hemisphere by Europeans," from Modern Latin Americanus, from America (q.v.). The original sense is now Native Americans; the sense of "resident of North America of European (originally British) descent" is from 1765.
American (adj.) Look up American at Dictionary.com
1590s, "pertaining to the Western Hemisphere and its aboriginal inhabitants," from Modern Latin Americanus, from America (q.v.); the sense of "pertaining to the residents of North America of European (originally British) descent" is first recorded 1640s; later "pertaining to the United States." French Américain, Spanish and Italian Americano, German Amerikanisch. Fem. form Americaness attested from 1838. The American beauty rose so called from 1887. American English as a sub-language attested from 1806; Amerenglish is from 1974.