僭する[sensuru] to usurp boastfully
僭位[seni] usurpation of a throne
僭越[senetsu] presumptuous
僭王[senou] usurper king
僭主[senshu] usurper

僭取[senshu] usurpation
僭称[senshou] pretension
僭上[senjou] audacity
僭用[senyou] using something belonging exclusively to someone else
僭上越権[senjouekken] exceeding (overstepping) one's powers (competence, authority)