alien (n.) Look up alien at Dictionary.com
"foreigner, citizen of a foreign land," early 14c., from alien (adj.) or from noun use of the adjective in French and Latin. In the science fiction sense "being from another planet," from 1953.
alien (adj.) Look up alien at Dictionary.com
c. 1300, "strange, foreign," from Old French alien "strange, foreign;" as a noun, "an alien, stranger, foreigner," from Latin alienus "of or belonging to another, not one's own, foreign, strange," also, as a noun, "a stranger, foreigner," adjective from alius (adv.) "another, other, different," from PIE root *al- (1) "beyond."

Meaning "residing in a country not of one's birth" is from mid-15c. Sense of "wholly different in nature" is from 1670s. Meaning "not of this Earth" first recorded 1920. An alien priory (c. 1500) is one owing obedience to a mother abbey in a foreign country.