adj. Owing political allegiance to another country or government; foreign: alien residents. adj. Belonging to, characteristic of, or constituting another and very different place, society, or person; strange. See Synonyms at foreign.adj. Dissimilar, inconsistent, or opposed, as in nature: emotions alien to her temperament. n. An unnaturalized foreign resident of a country. Also called noncitizen.n. A person from another and very different family, people, or place.n. A person who is not included in a group; an outsider.n. A creature from outer space: a story about an invasion of aliens. n. Ecology An organism, especially a plant or animal, that occurs in or is naturalized in a region to which it is not native.v. Law To transfer (property) to another; alienate.