Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
cĭsĭum, ii, n., a light two-wheeled vehicle, a cabriolet (vehiculi biroti genus, Non. p. 86, 30), Cic. Phil. 2, 31, 77; id. Rosc. Am. 7, 19; Vitr. 10, 1, 6; Aus. Ep. 8, 6; gen. cisi, Verg. Cat. 8, 3 Burm.; cf. Becker, Gall. 3, p. 9; Dict. of Antiq.