Lewis & Short

ĭn-ŏpīnābĭlis, e, adj.,

  1. I. not to be supposed or expected, inconceivable: latebra, Gell. 17, 9, 18: id (dictum), id. 11, 18, 11: res, Aur. Vict. Caes. 39.
  2. II. Esp., rhet. t. t., surprising, paradoxical: infames materias, sive quis mavult dicere inopinabiles, quas Graeci ἀδόξους ὑποθέσεις appellant, veteres adorti sunt, Gell. 17, 12, 1.
    Adv.: inŏpīnābĭlĭter, unexpectedly, Cassiod. Hist. Eccl. 1, 3; 8, 1.