Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
merda, ae, f. [etym. dub.; cf. Gr. μορύσσειν, to defile], dung, ordure, excrement: corvorum, Hor. S. 1, 8, 37; Mart. 3, 17, 6; Veg. 2, 8, 4; Phaedr. 4, 17, 25.