DIAPASON (Gr. &It racCov, through all), a term in music originally denoting the interval of an octave. The Greek is an abbreviation of 7) sta racrc7o xopoCov av,u0covi.a, a consonance through all the tones of the scale. In this sense it is only used now, loosely, for the compass of an instrument or voice, or for a harmo nious melody. The name is given to the two foundation stops of an organ, the open and the stopped diapason (see ORGAN) and to a standard of musical pitch, as in the French diapason normal (see PITCH, MUSICAL).