Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Sĭcyon, ōnis (abl. e, rarely i), f. (but masc. Cic. Att. 1, 13, 1), = Σικυών, the capital of the territory of Sicyonia in the Peloponnesus (now Vasiliko), near the isthmus, sometimes considered as belonging to Achaia, abounding in olive-trees, the birthplace of Aratus, Mel. 2, 3, 10; Plin. 4, 5, 6, § 12; Cic. Off. 2, 23, 81; id. Fam. 13, 21; id. Att. 1, 13, 1; Ov. Ib. 315; id. P. 4, 15, 10; Plaut. Curc. 3, 25; id. Merc. 3, 4, 62 al.
Abl. Sicyoni, Plaut. Cist. 1, 3, 8; 1, 3, 42; id. Ps. 4, 2, 38; and Sicyone, id. Cist. 1, 2, 11; id. Ps. 4, 7, 80; Cic. Fam. 13, 21, 1 and 2.
Hence, Sĭcyōnĭus, a, um, adj., of or belonging to Sicyon, Sicyonian: ager, Liv. 33, 15: magistratus, Cic. Verr. 2, 1, 17, § 44: Aratus, id. Off. 2, 23, 81: calcei, a lcind of soft shoes, id. de Or. 1, 54, 231: baca, olives, Verg. G. 2, 519: ager, Liv. 43, 15.
As substt.