Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
aurĭ-pigmentum, i, n. [aurum], orpiment; composed of arsenic, sulphur, and earth, of a brilliant yellow color, Vitr. 7, 7; Cels. 5, 5; Plin. 33, 4, 22, § 79.