n. In music: In the ancient Greek system, the octave.n. The entire compass of a voice or an instrument.n. Correct tune or pitch.n. n. A rule by which organ-pipes, flutes, etc., are constructed, so as to produce sounds of the proper pitch.n. A fixed standard of pitch, as the French diapason normal, according to which the A next above middle C has 435 vibrations per second. See pitch.n. A tuning-fork.n. In organ-building, the two principal foundation-stops, called respectively the open diapason and the stopped diapason. The open diapason has metal pipes of large scale, open at the top, giving that full, sonorous, majestic tone which is the typical organ-tone. The stopped diapason has wooden pipes of large scale, stopped at the top by wooden plugs, giving that powerful, flute-like tone which is the typical flute-tone of the organ. The most important mutation-stops of the open-diapason species are the double open diapason, sounding the octave below the key struck; the principal or octave, sounding the octave above; and the fifteenth, sounding the second octave above. Those of the stopped-diapason species are the bourdon, sounding the octave below; the flute, sounding the octave above; and the piccolo, sounding the second octave above. Many varieties of each of these occur. See stop.