Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Ērillus (Hērillus), i, m., a Stoic philosopher of Carthage, who flourished about B. C. 260, Cic. Fin. 2, 13, 43; id. Tusc. 5, 30, 85; Lact. 3, 7, 8.,
Hence, Ērillĭi (Her-), ōrum, m., the disciples of Erillus, Cic. de Or. 3, 17, 62.