noun the entire compass of tones.
2. diapason ·noun concord, as of notes an octave apart; harmony.
3. diapason ·noun a standard of pitch; a tuning fork; as, the french normal diapason.
4. diapason ·noun the octave, or interval which includes all the tones of the diatonic scale.
5. diapason ·noun one of certain stops in the organ, so called because they extend through the scale of the instrument. they are of several kinds, as open diapason, stopped diapason, double diapason, and the like.