indubius

in-dŭbĭus, a, um, adj.,

not doubtful , certain (post-Aug.): innocentia plurimorum, Tac. A. 14, 45: exempla, Quint. 5, 13, 24.— Hence, adv.: indŭbĭē , doubtlessly , Cassiod. Fragm. in Auct. Class. Tom. 3, 355 Mai.