diapason(redirected from open diapason)
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1. either of two stops (open and stopped diapason) usually found throughout the compass of a pipe organ that give it its characteristic tone colour
2. the compass of an instrument or voice
3. chiefly in French usage
a. a standard pitch used for tuning, esp the now largely obsolete one of A above middle C = 435 hertz, known as diapason normal
b. a tuning fork or pitch pipe
4. (in classical Greece) an octave