Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
optātīvus, a, um, adj. [opto], of or belonging to a wish, expressing a wish, optative (post-class.): modus optativus, the optative, Diom. p. 330 P.: adverbia, Mart. Cap. 3, § 310.