Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
pĕtax, ācis, adj. [peto], catching at, striving after, greedy for any thing; with gen. (post-class.): ornatūs petax, Fulg. Myth. 2, 1: potentiae petax, id. ib. 2, 3.
Hence, adv. comp.: pĕtācĭus, more greedily, Avien. Progn. 432.