diapason

[lettered]

di·a·pa·son

   
[dahy-uh-pey-zuhn, -suhn]

–noun
1. a full, rich outpouring of melodious sound.
2. the compass of a voice or instrument.
3. a fixed standard of pitch.
4. either of two principal timbres or stops of a pipe organ, one of full, majestic tone (open diapason) and the other of strong, flutelike tone (stopped diapason).
5. any of several other organ stops.
6. a tuning fork.