Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
dē-rōsus, a, um, Part. [derodo, not in use], gnawed away, nibbled: clipeos a muribus, * Cic. Div. 1, 44, 99: vitis a cochleis, Plin. 11, 37, 62, § 164: ficus a locustis, id. 17, 25, 38, § 241.