ETYM Old Eng. treble threefold, Old Fren. treble, treible, Latin triplus. Related to Triple.
Three times as great or many; SYN. threefold, triple.
In music, the highest register of a boy's voice (approximately equivalent in range to the soprano voice of a woman), about F4–C6, or the highest-pitched member of a family of instruments, for example the treble viol. The term is also used to refer to the right hand of a piano piece.

To sing treble.

1. The highest voice part in harmonic music; soprano; one that performs a treble part; also; a member of a family of instruments having the highest range; a high-pitched or shrill voice, tone, or sound; the upper half of the whole vocal or instrumental tonal range — compare bass; the higher portion of the audio frequency range in sound recording and broadcasting
2. Something treble in construction, uses, amount, number, or value