n. Mus.
1. the compass of a voice or musical instrument.
2 a fixed standard of musical pitch.
3 (in full open or stopped diapason) either of two main organ-stops extending through the organ's whole compass.
4 a a combination of notes or parts in a harmonious whole. b a melodious succession of notes, esp. a grand swelling burst of harmony.
5 an entire compass, range, or scope.
Etymology: ME in sense 'octave' f. L diapason f. Gk dia pason (khordon) through all (notes)