diapason

noun

1. The musical octave.

   “2 to 1, which is a duple ratio, forms the [symphony] diapason”

2. (broadly, literary)The range or scope of something, especially of notes in a scale, or of a particular musical instrument.

   “The glories and the beauties of form, color, and sound unite in the Grand Canyon—forms unrivaled even by the mountains, colors that vie with sunsets, and sounds that span the diapason from tempest to tinkling raindrop, from cataract to bubbling fountain.”

   “the piano curving like a conch, corollas giving out diapasons of light […]”

3. A tonal grouping of the flue pipes of a pipe organ.
4. One of the lowest strings on an archlute, theorbo, chitarrone, or similar bass lute-family instrument, usually unfrettable.
5. A harmonious outpouring of sound.

   “That we on Earth with undiscording voice May rightly answer that melodious noise; As once we did, till disproportion'd sin Jarr'd against natures chime, and with harsh din Broke the fair musick that all creatures made To their great Lord, whose love their motion sway'd In perfect Diapason, whilst they stood In first obedience, and their state of good.”

   “he could hear nothing except the rattle of the crickets and the swelling diapason of the frogs […]”