Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
cessim (cossim), adv. [cesso; cf. coxim], bending or turning in; hence, also, turned backwards, backwards (mostly anteand post-class.): cum domum ab Ilio cessim revertero, Varr. ap. Non. p. 247, 26; p. 276, 9: cessim ire, Dig. 9, 2, 52, § 2; Just. 2, 12, 7: lagena orificio cessim (obliquely) dehiscente patescens, App. M. 2, p. 121, 8.
cossim, adv., v. cessim.