The Collaborative International Dictionary of English v.0.48:

Ouster \Oust"er\, n. [Prob. fr. the OF. infin. oster, used
   substantively. See Oust.]
   A putting out of possession; dispossession; disseizin; -- of
   a person.
   [1913 Webster]

         Ouster of the freehold is effected by abatement,
         intrusion, disseizin, discontinuance, or deforcement.
                                                  --Blackstone.
   [1913 Webster]

   2. Expulsion; ejection; as, his misbehavior caused his ouster
      from the party; -- of a person, from a place or group.
      [PJC]

   Ouster le main. [Ouster + F. la main the hand, L. manus.]
      (Law) A delivery of lands out of the hands of a guardian,
      or out of the king's hands, or a judgement given for that
      purpose. --Blackstone.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Dispossession \Dis`pos*ses"sion\, n. [Cf. F. d['e]possession.]
   1. The act of putting out of possession; the state of being
      dispossessed. --Bp. Hall.
      [1913 Webster]

   2. (Law) The putting out of possession, wrongfully or
      otherwise, of one who is in possession of a freehold, no
      matter in what title; -- called also ouster.
      [1913 Webster]

WordNet (r) 3.0 (2006):

ouster
    n 1: a person who ousts or supplants someone else [syn:
         ouster, ejector]
    2: a wrongful dispossession
    3: the act of ejecting someone or forcing them out [syn:
       ouster, ousting]

Moby Thesaurus II by Grady Ward, 1.0:

26 Moby Thesaurus words for "ouster":
   booting out, bouncer, chucker, chucker-out, defenestration,
   detrusion, discharge, dislodgment, dispossession, ejection,
   ejectment, ejector, eviction, evictor, expeller, expulsion,
   extrusion, jettison, kicking downstairs, obtrusion, ousting,
   rejection, removal, the boot, the bounce, throwing out



Bouvier's Law Dictionary, Revised 6th Ed (1856):

OUSTER, torts. An ouster is the actual turning out, or keeping excluded, the
party entitled to possession of any real property corporeal.
     2. An ouster can properly be only from real property corporeal, and
cannot be committed of anything movable; 1 Car. & P. 123; S. C. 11 Eng. Com.
Law R. 339; 2 Bouv. 1 Inst. n. 2348; 1 Chit. Pr. 148, note r; nor is a mere
temporary trespass considered as an ouster. Any continuing act of exclusion
from the enjoyment, constitutes an ouster, even by one tenant in common of
his co-tenant. Co. Litt. 199 b, 200 a. Vide 3 Bl; Com. 167; Arch. Civ. Pl.
6, 14; 1 Chit. Pr. 374, where the remedies for an ouster are pointed out.
Vide Judgment of Respondent Ouster.