DIAPASON (Gr. &a raccov, through all)  , a term in music, originally for an interval of an octave . The Greek is an abbreviation of it &a ravWV Xopbav ovµikovia, 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 harmonious 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) .