The Collaborative International Dictionary
Tridiapason
Tridiapason \Tri*di`a*pa"son\, n. [Pref. tri- + diaposon.] (Anc.
Mus.)
A triple octave, or twenty-second.
--Busby.
Wiktionary
tridiapason
n. (context music historical English) A triple octave, or twenty-second.