Lewis & Short

ĭn-effĭcax, ācis, adj., ineffectual, inefficient (post-Aug.).

        1. (α) With gen.: vox inefficax verborum, unproductive of, unable to produce, Sen. Ira, 1, 3.
        2. (β) Absol.: ratio, Sen. Ira, 1, 10: dii, id. Ben. 4, 4.
          Comp., Plin. 34, 11, 25, § 109: parentes inefficacissimi, i. e. very weak, Inscr. ap. Grut. 415, 10.
          Adv.: ĭneffĭcācĭter, ineffectually, in vain, Dig. 49, 8, 2; Cod. Just. 6, 35, 2; Symm. Ep. 6, 53.