What is the meaning of Diapason?

The musical octave.

The range or scope of something, especially of notes in a scale, or of a particular musical instrument.

A tonal grouping of the flue pipes of a pipe organ.

A harmonious outpouring of sound.

range, diapason

a tuning fork

tuning fork

diapason

tone (of a voice, conversation, etc.)

Source: wiktionary.org