The Collaborative International Dictionary of English v.0.48:

Alien \Al"ien\, a. [OF. alien, L. alienus, fr. alius another;
   properly, therefore, belonging to another. See Else.]
   1. Not belonging to the same country, land, or government, or
      to the citizens or subjects thereof; foreign; as, alien
      subjects, enemies, property, shores.
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   2. Wholly different in nature; foreign; adverse; inconsistent
      (with); incongruous; -- followed by from or sometimes by
      to; as, principles alien from our religion.
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            An alien sound of melancholy.         --Wordsworth.
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   Alien enemy (Law), one who owes allegiance to a government
      at war with ours. --Abbott.
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The Collaborative International Dictionary of English v.0.48:

Alien \Al"ien\, n.
   1. A foreigner; one owing allegiance, or belonging, to
      another country; a foreign-born resident of a country in
      which he does not possess the privileges of a citizen.
      Hence, a stranger. See Alienage.
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   2. One excluded from certain privileges; one alienated or
      estranged; as, aliens from God's mercies.
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            Aliens from the common wealth of Israel. --Ephes.
                                                  ii. 12.
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The Collaborative International Dictionary of English v.0.48:

Alien \Al"ien\, v. t. [F. ali['e]ner, L. alienare.]
   To alienate; to estrange; to transfer, as property or
   ownership. [R.] "It the son alien lands." --Sir M. Hale.
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         The prince was totally aliened from all thoughts of . .
         . the marriage.                          --Clarendon.
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WordNet (r) 3.0 (2006):

alien
    adj 1: not contained in or deriving from the essential nature of
           something; "an economic theory alien to the spirit of
           capitalism"; "the mysticism so foreign to the French mind
           and temper"; "jealousy is foreign to her nature" [syn:
           alien, foreign]
    2: being or from or characteristic of another place or part of
       the world; "alien customs"; "exotic plants in a greenhouse";
       "exotic cuisine" [syn: alien, exotic]
    n 1: a person who comes from a foreign country; someone who does
         not owe allegiance to your country [syn: foreigner,
         alien, noncitizen, outlander] [ant: citizen]
    2: anyone who does not belong in the environment in which they
       are found [syn: stranger, alien, unknown] [ant:
       acquaintance, friend]
    3: a form of life assumed to exist outside the Earth or its
       atmosphere [syn: extraterrestrial being,
       extraterrestrial, alien]
    v 1: transfer property or ownership; "The will aliened the
         property to the heirs" [syn: alien, alienate]
    2: arouse hostility or indifference in where there had formerly
       been love, affection, or friendliness; "She alienated her
       friends when she became fanatically religious" [syn:
       estrange, alienate, alien, disaffect]

The Devil's Dictionary (1881-1906):

ALIEN, n.  An American sovereign in his probationary state.