Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† īrĭnus, a, um, adj., = ἴρινος, of or belonging to the plant iris, iris-: sucus, Plin. 30, 14, 43, § 142: unguentum, Cels. 5, 18, 8.
Hence, subst.: īrĭnum, i, n., ointment made from the iris, iris-ointment, Cels. 3, 18; Plin. 20, 17, 71, § 182.