usurper Definition

usurp
verb usurped, usurping

1. To take possession of (eg land) or assume (eg power, authority, a title, etc) by force, without right or unjustly.

Thesaurus: annex, appropriate, commandeer, seize, steal, take over, assume, wrest, arrogate, confiscate.
2. To encroach on something (eg someone else's rights, territory, sphere of interest, etc).

Derivative: usurpation
noun

Derivative: usurper
noun

Etymology: 14c: from French usurper, from Latin usurpare to take possession for use.