Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Thăsus or -os, i, f., = Θάσος, an island in the north of the Ægean Sea, off the coast of Thrace, now Thaso, Mel. 2, 7, 8; Plin. 4, 12, 23, § 73; Cic. Pis. 36, 89; Auct. Her. 4, 54, 68; Liv 33, 30; 33, 35; Stat. S. 1, 5, 34; 2, 2, 92 al.
Hence, Thăsĭus, a, um, adj., of or belonging to Thasus, Thasian: nuces, Varr. ap. Gell. 7, 16, 5; Plin. 15, 22, 24, § 90: vinum, Poët. ap. Plin. 14, 14, 16, § 95: vites, Verg. G. 2, 91: lapis, Sen. Ep. 86, 5.