What does Sūsa mean in Latin?

Sūsa, a proper noun, means “Susa (a former city in Iran)”.

What is the genitive of Sūsa?

The genitive singular is Sūsōrum. Sūsa is neuter, second declension.

proper noun · neutersecond declension

Sūsa n pl (genitive Sūsōrum)

Sūsa, ōrum, n., = Σοῦσα, τά,

I. the ancient capital of Persia, now prob. Soos, Plin. 6, 27, 31, § 133; Prop. 2, 13 (3, 4), 1; Curt. 5, 1, 7.—Hence,

A. Sūsĭānē, ēs, f., the province of Susiana or Susiane, in which Susa was situated, now Khuzistan, Plin. 6, 27, 31, § 133.—

B. Sūsĭāni, ōrum, m., the inhabitants of Susa or of Susiana, Plin. 6, 27, 31, § 133; Curt. 5, 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.

Borrowed from Ancient Greek Σοῦσα (Soûsa).