Synonyms for Alien:

adj.

all (adjective)
foreign.
different (adjective)
unusual.
extraneous (adjective)
outlandish, inadmissible, detached, dissociated, irrelevant, nonessential, eerie, impertinent, disconnected, foreign-born, outer, unrelated, segregated, disaffiliated, exotic, other, inappropriate, separate, extraterrestrial, disjoint, strange, extrinsic, inapplicable, external, unessential, Unallied, outside, separated, estranged, extraneous, removed, unaffiliated, foreign, parenthetical, immaterial.
foreign (adjective)
opposed, extraneous, extrinsic, separate, remote, exotic, unusual, estranged, inappropriate.
unrelated (adjective)
remote, irrelevant, segregated, unaffiliated, dissociated, disenfranchised, inapplicable, extraneous, separate, detached, unrelated, foreign, disjoint, Unallied.

n.

offbeat, out of the ordinary, remarkable, notable, unique, odd, surprising, special. opposed, study at, overseas, different, gaijin, dissimilar, unusual, repugnant. MIGR, newcomer. aeronaut (noun)
flier, aeronaut, aviator, passenger, astronaut, spaceman, martian, copilot, cosmonaut, astro-navigator, captain, airman, rocketeer, balloonist, pilot.
alien (noun)
disaffect, foreigner, noncitizen, strange, extraterrestrial, alienate, foreign, extraterrestrial being, outlander, estrange, stranger, extrinsic, exotic, unknown.
foreign being (noun)
newcomer, noncitizen, immigrant, refugee, foreigner, migrant, stranger.
foreigner (noun)
migrant, outlander, foreigner, refugee, expatriate, immigrant, stranger.
person (noun)
outlander, foreigner, noncitizen.

v.

possession (verb)
alienate.

Other synonyms:

overseas, android, beam up, newcomer, cyborg, gaijin, beam down, repugnant, earthling, cyberpunk. ET. Other relevant words:
estrange, different, odd, disaffect, unusual, opposed, alienate, dissimilar, newcomer, unique, overseas, cyberpunk, ET, remarkable, noncitizen, extraterrestrial being, offbeat, gaijin, unknown, repugnant.

Usage examples for alien

  1. It was final this time, for the two alien enemies once out of it would not be let into England again till after the war. – Christopher and Columbus by Countess Elizabeth Von Arnim
  2. They were akin to them, alien to their parents. – Tropic Days by E. J. Banfield