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.
late 14c., "inhabitant of Asia (Minor)," from Latin Asianus (adjective and noun, "belonging to the province of Asia;" "an inhabitant of Asia"), from Greek Asianos "Asiatic," from Asia (see Asia). Ousted Asiatic as the preferred term mid-20c.
The term "Asiatic" has come to be regarded with disfavour by those to whom it is applied, and they feel entitled to be brought into line with usage in regard to Europeans, Americans and Australians. [Times Literary Supplement, Feb. 6, 1953]
As an adjective in English, "of or pertaining to Asia," from 1560s; common from c. 1930. Related: Asianic (1879).
Others are reading
<a href="https://www.etymonline.com/word/Amerasian">Etymology of Amerasian by etymonline</a>
Harper, D. (n.d.). Etymology of Amerasian. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/Amerasian