The Collaborative International Dictionary of English v.0.48:

Oust \Oust\, v. t. [imp. & p. p. Ousted; p. pr. & vb. n.
   Ousting.] [OF. oster, F. [^o]ter, prob. fr. L. obstare to
   oppose, hence, to forbid, take away. See Obstacle, and cf.
   Ouster.]
   1. To take away; to remove.
      [1913 Webster]

            Multiplication of actions upon the case were rare,
            formerly, and thereby wager of law ousted. --Sir M.
                                                  Hale.
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   2. To eject; to expel; to turn out. --Blackstone.
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            From mine own earldom foully ousted me. --Tennyson.
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The Collaborative International Dictionary of English v.0.48:

Oust \Oust\, n.
   See Oast.
   [1913 Webster]

WordNet (r) 3.0 (2006):

oust
    v 1: remove from a position or office; "The chairman was ousted
         after he misappropriated funds" [syn: oust, throw out,
         drum out, boot out, kick out, expel]
    2: remove and replace; "The word processor has ousted the
       typewriter"