means A usurper is someone who seizes power, a position, or a right by force or without legitimate claim — most classically a crown.

from From Latin usurpare, "to seize for use, take possession of," itself thought to come from usu (by use) plus rapere (to seize, grab) — the same rapere that gives us "rapture" and "rapacious." So buried in the word is a thief's logic: to use a thing is to own it. It came into English through Old French usurper in the medieval period, already wearing its crown of stolen authority.