/ ˈeɪliən; NAmE / adjective , noun
■ adjective
1.
alien (to sb/sth) strange and frightening; different from what you are used to
SYN hostile :
an alien environment
In a world that had suddenly become alien and dangerous, he was her only security.
2.
(often disapproving ) from another country or society; foreign :
an alien culture
3.
alien to sb/sth ( disapproving ) not usual or acceptable :
The idea is alien to our religion.
Cruelty was quite alien to him.
4.
connected with creatures from another world :
alien beings from outer space
■ noun
1.
( NAmE also ˌnon-ˈcitizen ) ( law or technical ) a person who is not a citizen of the country in which they live or work :
an illegal alien
—compare resident alien
2.
a creature from another world :
aliens from outer space
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WORD ORIGIN
Middle English : via Old French from Latin alienus belonging to another, from alius other.