Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
con-vulsĭo (-vols-), ōnis, f. [convello], in medic. lang., cramp, convulsion, Scrib. Comp. 165; Plin. 20, 15, 60, § 168; 29, 3, 13, § 55.