Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Sīla, ae, f., a large forest in the country of the Bruttii, which yielded great quantities of pitch, Cic. Brut. 22, 85; Sall. Fragm. ap. Serv. Verg. A. 12, 715 (H. 4, 7 Dietsch); Plin. 3, 5, 10, § 74; Verg. G. 3, 219; id. A. 12, 715.
Hence, Sīlānus, a, um, adj., of or belonging to the forest of Sila: caseus, Cassiod. Var. 12, 12.