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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, adv.: nĕcŏpīnanter, unexpectedly, unawares: necopinanter, ἀπροσδοκήτως, Gloss. Philox.