diapason

1. (music) The musical octave.Examples: "2 to 1, which is a duple ratio, forms the [symphony] diapason"

2. (by extension, literary) The range or scope of something, especially of notes in a scale, or of a particular musical instrument.Examples: "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 […]"Synonyms: range, scopebroadlyliterary

3. (music) A tonal grouping of the flue pipes of a pipe organ.

4. (music) One of the lowest strings on an archlute, theorbo, chitarrone, or similar bass lute-family instrument, usually unfrettable.