alien (aliens plural )
1 adj Alien means belonging to a different country, race, or group, usually one you do not like or are frightened of.
FORMAL usu ADJ n (disapproval)
(=foreign)
He said they were opposed to the presence of alien forces in the region.
2 adj You use alien to describe something that seems strange and perhaps frightening, because it is not part of your normal experience.
usu ADJ n
(=unfamiliar)
His work offers an insight into an alien culture.
3 adj If something is alien to you or to your normal feelings or behaviour, it is not the way you would normally feel or behave.
FORMAL v-link ADJ to n
(=foreign, unfamiliar)
Such an attitude is alien to most businessmen.
4 n-count An alien is someone who is not a legal citizen of the country in which they live.
FORMAL or, LEGAL
(=foreigner)
5 n-count In science fiction, an alien is a creature from outer space.