Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
cāso, v. casso.
2. casso (caso), avi, atum, 1, v. n., rare collat. form of quasso (only in Plautus), to shake, waver: ubi bacchabatur aula, cassabant cadi, Plaut. Mil. 3, 2, 41; cf. v. 37: capitibus cassantibus, id. Bacch. 2, 3, 71; cf. quasso, II.