noun (n)

• entry to another's property without right or permission(noun.act)

  Synonym:
  encroachment, intrusion, trespass, violation
  

  source: wordnet30
• wrongfully seizing and holding (an office or powers) by force (especially the seizure of a throne or supreme authority)(noun.act)

  Example:
  A succession of generals who ruled by usurpation.
  

  source: wordnet30
• The act of usurping, or of seizing and enjoying; an authorized, arbitrary assumption and exercise of power, especially an infringing on the rights of others; specifically, the illegal seizure of sovereign power; -- commonly used with of, also used with on or upon; as, the usurpation of a throne; the usurpation of the supreme power.(noun)

  source: webster1913