Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† mŏnŏsyllăbus, a, um, adj., = μονοσύλλαβος, monosyllabic (post-Aug.): VOX, Mart. Cap. 3, § 269; 5, § 520.
As subst., a monosyllable: mŏnŏsyllabon, i, n. (sc. verbum), Aus. Idyll. Lit. Monosyll. 13: monosyllaba, sc. verba, Quint. 9, 4, 42; Mart. Cap. 3, § 294.