Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
vērātrum, i, n., a plant, hellebore, Plin. 25, 5, 21, § 52; Gell. 17, 5, 6; Cels. 2, 12 sq.; 3, 23; Lucr. 4, 640; Pers. 1, 51.