Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
querquĕrus or quercĕrus, a, um, adj. [cf. Gr. καρκαίρω, to tremble], cold to trembling, shivering (ante- and post-class.): querqueram frigidam cum tremore a Graeco κάρκαρα certum est dici, unde et carcer. Lucilius: Jactans me ut febris querquera, the ague, Paul. ex Fest. p. 256 Müll.; so, febris querquera, Plaut. Fragm. ap. Prisc. p. 719 P.: febris rapida et quercera, Gell. 20, 1, 26; also, absol.: querquĕra, ae, f., the ague: querqueras sanare, Arn. 1, 28; App. Mag. p. 297, 14 (al. querquerum).