Noun
The octave, or interval which includes all the tones of the diatonic scale.
Concord, as of notes an octave apart; harmony.
The entire compass of tones.
A standard of pitch; a tuning fork; as, the French normal diapason.
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.
Source: Webster's dictionaryFrom harmony, from heavenly harmony, This universal frame began: From harmony to harmony Through all the compass of the notes it ran, The diapason closing full in Man. John Dryden
The vox angelica replied - The shadows flee away! Our house-beams were of cedar. Come in, with boughs of may! The diapason deepened it - Before the darkness fall, We tell you He is risen again! Our God hath burst His prison again! The Lord of Life is risen again; and Love is Lord of all. Alfred Noyes