Lewis & Short

Sūsa, ōrum, n., = Σοῦσα, τά, the ancient capital of Persia, now prob. Soos, Plin. 6, 27, 31, § 133; Prop. 2, 13 (3, 4), 1; Curt. 5, 1, 7.
Hence,

  1. A. Sūsĭānē, ēs, f., the province of Susiana or Susiane, in which Susa was situated, now Khuzistan, Plin. 6, 27, 31, § 133.
  2. B. Sūsĭāni, ōrum, m., the inhabitants of Susa or of Susiana, Plin. 6, 27, 31, § 133; Curt. 5, 3, 3.
  3. C. Sūsis, ĭdis, adj. f., of or belonging to Susa, Susian, Persian: ora, Sid. poët. Ep. 7, 17: aula, id. ib. 8, 9.