Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† lathyris, ĭdis, f. (collat. form, lā-thyr, Ser. Samm. 1099), = λαθυρίς, a plant, a kind of wolf’s-milk, Plin. 27, 11, 71, § 95.