Lewis Short
(adjective) : ūsurpātīvus, a, um, usurpo, II. B. 2.
* Wrongly used, unusual, improper, usurpative (late Lat.): species verborum,Diom. p. 389 P.; Macr. Diff. Verb. p. 2764 ib. —Adv.: ūsurpātīvē, in an unusual manner, improperly, wrongly: usurpative ait hordea,Serv. ad Verg. G. 1, 210; id. ad Verg. A. 7, 289.
Charlton T. Lewis, Charles Short, A Latin Dictionary