Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
pĕtīlus, a, um, adj., thin, slender (anteclass.): petilum tenue et exile, Non. 149, 7 sq.; Lucil. and Plaut. ap. Non. 1. 1.: petilam suram, siccam et substrictam vulgo interpretantur: Scaevola ait, ungulam albam equi ita dici, Fest. p. 205 Müll.