Real Dictionary

alien
Alien means belonging to a different country, race, or group, usually one you do not like or are frightened of.
You use alien to describe something that seems strange and perhaps frightening, because it is not part of your normal experience.
adjective: If something is alien to you or to your normal feelings or behaviour, it is not the way you would normally feel or behave.

alien in American English
belonging to another country or people; foreign
adjective: residing under a government or in a country other than that of one's birth without having or obtaining the status of citizenship there
noun: a resident born in or belonging to another country who has not acquired citizenship by naturalization (distinguished from citizen)

alien in British English
adjective: unnaturalized; foreign
noun: a person owing allegiance to a country other than that in which he or she lives; foreigner
verb: to transfer (property, etc) to another