Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† mŏnoptōta, ōrum, n., = μονόπτωτα, in the later grammarians, nouns which have but one case-ending, monoptotes, Diom. p. 288 P.; Prisc. p. 672 ib. et saep.; Mart. Cap. 3, § 242 al.