u·surp / yoōˈsərp/ • v. [tr.] take (a position of power or importance) illegally or by force: Richard usurped the throne. ∎ take the place of (someone in a position of power) illegally: supplant: the Hanoverian dynasty had usurped the Stuarts. ∎ [intr.] (usurp on/upon) archaic encroach or infringe upon (someone's rights): the Church had usurped upon the domain of the state.DERIVATIVES: u·sur·pa·tion / ˌyoōsərˈpāshən/ n.u·surp·er n.