Lewis Short
(adj.adv.) : ĭn-ŏpīnans, antis, adj.
* Not expecting, unaware (freq. in the historians; not in Cic.): inscios inopinantesque Menapios oppresserunt,Caes. B. G. 4, 4: impeditos et inopinantes aggressus,id. ib. 1, 12: imprudente atque inopinante Curione,id. B. C. 2, 3: rex in potestatem inopinanti (ei) venerat,Nep. Dat. 3, 4: suis inopinantibus,Liv. 27, 48, 14.— Hence, adv.: ĭnŏpīnanter, unexpectedly, Suet. Tib. 60.
Charlton T. Lewis, Charles Short, A Latin Dictionary