Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
disceptātrix, īcis, f. [disceptator], a female umpire, arbitrator, judge (very rare): dialectica veri et falsi quasi disceptatrix et judex, * Cic. Ac. 2, 28, 91; Lampr. Commod. 5.