Pronunciation: (āl'yun, ā'lē-un),[key] —n. 1. a resident born in or belonging to another country who has not acquired citizenship by naturalization (distinguished from citizen).
2. a foreigner.
3. a person who has been estranged or excluded.
4. a creature from outer space; extraterrestrial.
—adj. 1. residing under a government or in a country other than that of one's birth without having or obtaining the status of citizenship there.
2. belonging or relating to aliens: alien property. 3. unlike one's own; strange; not belonging to one: alien speech. 4. adverse; hostile; opposed (usually fol. by to or from): ideas alien to modern thinking. 5. extraterrestrial.