Lewis & Short

3. Ŏpūs, ūntis, f., = Ὀποῦς,

  1. I. a town of Locris, in Greece, now Kardhenitza, Liv. 28, 7; Ov. P. 1, 3, 73.
    Hence,
  2. II. Ŏpūn-tĭus, a, um, adj., Opuntian: sinus, Mel. 2, 3, 6; Plin. 4, 7, 12, § 27: Philodamus, of Opus, Cic. Verr. 2, 2, 44, § 109.
    In plur.: Ŏpūntĭi, ōrum, m., the inhabitants of Opus, the Opuntians, Liv. 28, 6 fin.