Lewis Short
(adj.adv.) : obreptīvus, a, um, adj.obrepo
* Secret, clandestine (post-class.): supplicatio,Symm. Ep. 5, 64; Cod. Th. 16, 10, 8.—Hence, adv.: obreptīvē, surreptitiously, clandestinely (post-class.): aut clanculo supplicare, Cod. Th. 16, 1, 4 fin.
Charlton T. Lewis, Charles Short, A Latin Dictionary