DISSYLLABLE is a 11 letter word that starts with D.
\Dis*syl"la*ble\ (?; 277), n. [F. dissyllabe, L. disyllabus, adj., of two syllables, fr. Gr. ?; di- = di`s- twice + ? syllable. See {Syllable}.] A word of two syllables; as, pa-per.
WordNet Dictionary