Source : Webster's Revised Unabridged Dictionary (1913)

Usurp \U*surp"\, v. i.
   To commit forcible seizure of place, power, functions, or the
   like, without right; to commit unjust encroachments; to be,
   or act as, a usurper.

         The parish churches on which the Presbyterians and
         fanatics had usurped.                    --Evelyn.

         And now the Spirits of the Mind Are busy with poor
         Peter Bell; Upon the rights of visual sense Usurping,
         with a prevalence More terrible than magic spell.
                                                  --Wordsworth.

Usurp \U*surp"\, v. t. [imp. & p. p. {Usurped}; p. pr. & vb. n.
   {Usurping}.] [L. usurpare, usurpatum, to make use of, enjoy,
   get possession of, usurp; the first part of usurpare is akin
   to usus use (see {Use}, n.): cf. F. usurper.]
   To seize, and hold in possession, by force, or without right;
   as, to usurp a throne; to usurp the prerogatives of the
   crown; to usurp power; to usurp the right of a patron is to
   oust or dispossess him.

         Alack, thou dost usurp authority.        --Shak.

         Another revolution, to get rid of this illegitimate and
         usurped government, would of course be perfectly
         justifiable.                             --Burke.

   Note: Usurp is applied to seizure and use of office,
         functions, powers, rights, etc.; it is not applied to
         common dispossession of private property.

   Syn: To arrogate; assume; appropriate.

Source : WordNet®

usurp
     v 1: seize and take control without authority and possibly with
          force; take as one's right or possession; "He assumed to
          himself the right to fill all positions in the town";
          "he usurped my rights"; "She seized control of the
          throne after her husband died" [syn: {assume}, {seize},
          {take over}, {arrogate}]
     2: take the place of; "gloom had usurped mirth at the party
        after the news of the terorist act broke"