Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† trĭsyllăbus, a, um, adj., = τρισύλλαβος, of three syllables, trisyllabic: verbum, Varr. L. L. 9, § 91 Müll.; Mart. Cap. 5, § 522; 3, § 169.