'Usurper' definitions:

Definition of 'usurper'

From: WordNet
noun
One who wrongfully or illegally seizes and holds the place of another [syn: usurper, supplanter]

Definition of 'Usurper'

From: GCIDE
  • Usurper \U*surp"er\, n. One who usurps; especially, one who seizes illegally on sovereign power; as, the usurper of a throne, of power, or of the rights of a patron. [1913 Webster]
  • A crown will not want pretenders to claim it, not usurpers, if their power serves them, to possess it. --South. [1913 Webster]

Synonyms of 'usurper'

From: Moby Thesaurus