Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
1. Sĕgesta, ae, f. [sibilated, acc. to Fest. p. 340 Müll., on account of the omen, from Ἔγεστα], an ancient city on the northern coast of Sicily, near Mount Eryx, Cic. Verr. 2, 4, 33, § 72; 2, 3, 40, § 92; Fest. p. 340 Müll.
Hence, Sĕgestānus, a, um, adj., of or belonging to Segesta, Segestan: civitas, Cic. Verr. 2, 3, 6, § 13; 2, 5, 32, § 83: diana, id. Or. 62, 210.
Substt.