Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
spernax, ācis, adj. [sperno], despising, showing contempt, contemptuous (post-Aug. and very rare): viri spernaces mortis, Sil. 8, 465: in admittendo consilio spernax, Sid. Ep. 4, 9.