Lewis Short
(adverb) : nĕc-ŏpīnans (also separately, nĕc ŏpīnans), antis
* Adj., not expecting, unaware (rare but class.), Ter. Heaut. 1, 2, 12: et necopinanti (tibi) mors ad caput accidit,Lucr. 3, 959 (Lachm., nec opinanti): Ariobarzanem necopinantem liberavi,Cic. Fam. 15, 4, 10; Phaedr. 5, 7, 8.—Hence, : nĕcŏpīnanter, unexpectedly, unawares: necopinanter, ἀπροσδοκήτως, Gloss. Philox.
Charlton T. Lewis, Charles Short, A Latin Dictionary