1911 Encyclopædia Britannica/Treble
TREBLE (a doublet of "triple", three-fold, from Lat. triplus, triple; cf. "double" from duplus), the term applies, in music, to the high or acute part of the musical system, as opposed to and distinguished from "bass," the lower or grave part. The middle C is the practical division between the parts. The word is also used as equivalent to the "soprano" voice, the highest pitch or range of the human voice, but generally it is confined to a boy's voice of this quality, "soprano" being used of the corresponding female voice. The treble-clef is the G-clef on the second line. The origin of this application of the term "treble," triplus treefold, to the highest voice or part is due to the fact that in the early plain-song the chief melody was given to the tenor, the second part to the alto (discantus) and where a third part (triplum) was added it was assigned to the highest voice, the soprano or treble.