Merriam-Webster's Collegiate® Dictionary, 11th Edition
TREBLE
I. noun
Etymology: Middle English, the highest part in a three-part composition, from treble, adjective
Date: 14th century
1. the highest voice part in harmonic music ; soprano , one that performs a treble part, a high-pitched or shrill voice, tone, or sound, the upper half of the whole vocal or instrumental tonal range, the higher portion of the audio frequency range in sound recording and broadcasting, something treble in construction, uses, amount, number, or value,
II. adjective see: triple
Date: 14th century
1. having three parts or uses ; threefold , triple in number or amount,
2. relating to or having the range or part of a treble, high-pitched , shrill , of, relating to, or having the range of treble in sound recording and broadcasting , trebly adverb
III. verb (trebled; trebling)
Date: 14th century
transitive verb to increase threefold, intransitive verb to sing treble, to grow to three times the size, amount, or number