- a creature from outer space; extraterrestrial.
- a resident of one country who was born in or owes allegiance to another country and has not acquired citizenship by naturalization in the country of residence (distinguished from citizen).
- a foreigner.
- a person who has been estranged or excluded.
- a plant or animal species not originating where it is found but introduced, sometimes accidentally, from its native environment elsewhere: Imported plants, seeds, or bulbs may harbor unwanted aliens such as foreign insects or the seeds of other plants.
- unlike one's own; strange; not belonging to one: In English class, our teacher treated all slang as alien speech.
- residing under a government or in a country other than that of one's birth without having or obtaining the status of citizenship there.
- belonging or relating to noncitizens: Under certain conditions, seizure of alien property is authorized.
- opposed; adverse; hostile (usually followed by to or from): Their manifesto is full of ideas alien to modern thinking.
- extraterrestrial (def. 1).
- (of a plant or animal species) not native; introduced from a different environment: The bullfrog is native to some Canadian provinces, but is an alien species in British Columbia.
- a person owing allegiance to a country other than that in which he lives; foreigner
- any being or thing foreign to the environment in which it now exists
- (in science fiction) a being from another world, sometimes specifically an extraterrestrial
- unnaturalized; foreign
- having foreign allegiance
- unfamiliar; strange
- repugnant or opposed (to)
- (in science fiction) of or from another world
- to transfer (property, etc) to another
