Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Scēpsis, is, f., = Σκῆψις, a town in Mysia, Plin. 5, 30, 32, § 122.
Hence, Scēp-sĭus, a, um, adj., of or belonging to Scepsis: Metrodorus, of Scepsis, Cic. Tusc. 1, 24, 59; Plin. 34, 7, 16, § 34; also called simply Scepsius, Ov. P. 4, 14, 38.