In music, the octave or interval which includes all the tones.

Among musical instrument-makers, a rule or scale by which they adjust the pipes of organs, the holes of flutes, in due proportion for expressing the several tones and semitones. Diapason-diapente, a compound consonance in a triple ratio, as to 9, consisting of 9 tones and a semitone, or 19 semitones; a twelfth. Diapason-diatessaron, a compound concord, founded on the proportion of 8 to 3, consisting of eight tones and a semitone. Diapason-ditone, a compound concord, whose terms are as 10 to 4, or 5 to 2. Diapason-semiditone, a compound concord, whose terms are in the proportion of 12 to 5.