Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Perseus.
Sīgēum, i, n., = Σίγειον, a promontory in Troas, and a town of the same name, where Achilles was buried, now Yenishehr, Mel. 1, 18, 3; Plin. 5, 30, 33, § 124; Cic. Arch. 10, 24; id. Fam. 5, 12, 7; Liv. 44, 28, 6.
Hence, Sīgēus (collat. form Sīgēïa tellus, Ov. H. 1, 33: Sigeïa litora, id. M. 13, 3), a, um, adj., of or belonging to Sigeum, Sigean: litora, Mel. 2, 7, 4; Ov. M. 12, 71: freta, Verg. A. 2, 312: campi, id. ib. 7, 294: profundum, Ov. M. 11, 197.