A Dictionary of Music and Musicians/Treble
TREBLE (Canto; Distant; Dessus). A general term applied to the highest voices in a chorus or other concerted vocal piece, and to the upper parts in concerted instrumental music; also to soprano voices generally. The treble clef is the G clef on the second line of the upper (our treble) stave; the eighth line of the great stave of eleven lines (Chiave di sol, chiave di violino; Clef de Sol).
Its etymology does not refer it to any special class of voice. It has been said to be a corruption of Triplum, a third part superadded to the Altus and Bassus (high and low). In this case it will have been sung by boys, who till then will have joined instinctively in congregational singing in unison with, or an octave above, the tenor. Another derivation is Thurible, the vessel in which incense is burnt in the services of the Roman Catholic Church, from the Latin Thuribulum. The portable thurible or censer was carried and swung by boys. But there is very strong doubt whether the thurible boys ever had any share in the vocal part of the church services; and if they did not, this theory is overturned. The thurible-bearers would surely be called, in describing a religious procession, 'the thurifers.' The derivation from Triplum seems therefore the more probable. At what time 'treble' may have found its way into English it is difficult to say. 'Childish treble,' as the voice of old age, appears in Shakspeare, and 'faint treble' used to be applied to what is commonly known as falsetto. English amateur pianists frequently call the right hand the treble hand. The word Triplum as a third part was of course introduced at a very early date, and marks a most important step in the progress of part-music.
The treble clef is a modification of the letter G. [Clef.] It is used for the violin, flute, hautboy, clarinet, horn, and trumpet; also in very high passages on the viola, violoncello, and bassoon. 𝄞𝄞 The double G clef has been used for tenor parts in choruses, the music being sung an octave lower than written; also for the horn in low keys. [Tenor.]