Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Sagalessos (Sagalass-), i, f., an important town of Pisidia, whose ruins are found near the mod. Aghtasan, Plin. 5, 27, 24, § 94.
Hence, Sagalassēnus, a, um, adj., of or belonging to Sagalessos: ager, Liv. 38, 15, 9.