Lewis & Short

ūsurpātōrĭus, a, um, adj. [usurpator], usurping, usurpatory: temeritas, Cod. Just. 10, 47, 8.
Adv.: ūsurpātōrĭē, presumptuously, pretentiously, Ambros. Hexaëm. 3, 15, n. 64; id. in Psa. 118, Serm. 5, § 23 al.