DIATONICK in Music, (composed of two Greek words, viz. the preposition dia, signifying a transition from one thing to another, and the substantive tonus, importing a given degree of tension or musical note), is indifferently applied to a scale or gammut, to intervals of a certain kind, or to a species of music, whether in melody or harmony, composed of these intervals. Thus we say the diatonic series, a diatonic interval, diatonic melody or harmony. As the diatonic scale forms the system of diatonic music, and consists of diatonic intervals, it will be necessary, for understanding the former, that we should explain the latter. See INTERVAL.