Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
mordex, ĭcis, adj. [mordeo], biting, gnawing: asini mordices, v. l., Plaut. Aul. 2, 3, 57 (better mordicus).
As subst.: Mor-dex, ĭcis, m., the biter, i. e. tooth, v. l. ap. App. M. 3, p. 140 (better mordicus, q. v.).