disdĭăpāsōn, indecl., = δὶς διὰ πασῶν,
a double octave in music, Mart. Cap. 9, § 950; Vitr. 5, 4, 9 al.; cf. diapason.
·noun An interval of two octaves, or a fifteenth; — called also bisdiapason. ...
Webster's Dictionary of the English Language