Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
pĕdĭtastellus, i, m. dim. [peditaster, not in use; formed like parasitaster, etc.; cf.: magistellus, cultellus, etc.], a wretched foot-soldier, tramp: at peditastelli quia erant, sivi viverent, Plaut. Mil. 1, 1, 50 Brix ad loc.