Lewis Short
ūsurpātor (noun M) : id.
* One who uses or takes possession unlawfully, a usurper of a thing (late Lat.): indebitae potestatis,Amm. 26, 7, 12: tanti nominis, Symm. Or. ap. Val. 1, 22.
* In gen., one who accomplishes: ardui operis, Jul. Sev. Syn. praef. 1.
Charlton T. Lewis, Charles Short, A Latin Dictionary