alien (adj.)

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 (mid 15c.) is one owing obedience to a religious jurisdiction in a foreign country.

alien (n.)

"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.

Definitions of alien
alien (n.)
a person who comes from a foreign country; someone who does not owe allegiance to your country;
Synonyms: foreigner / noncitizen / outlander
alien (n.)
anyone who does not belong in the environment in which they are found;
Synonyms: stranger / unknown
alien (n.)
a form of life assumed to exist outside the Earth or its atmosphere;
Synonyms: extraterrestrial being / extraterrestrial
alien (adj.)
not contained in or deriving from the essential nature of something;
an economic theory alien to the spirit of capitalism
Synonyms: foreign
alien (adj.)
being or from or characteristic of another place or part of the world;
alien customs
Synonyms: exotic
alien (v.)
transfer property or ownership;
The will aliened the property to the heirs
Synonyms: alienate