The definition of a treble clef is a symbol that is placed on every line of music to show the notes which will be sung or played by voices and instruments that can achieve higher notes.
(noun)An example of a treble clef is the symbol placed on piano music to show which notes should be played by the right hand of the pianist.
See treble clef in Webster's New World College Dictionary
See treble clef in American Heritage Dictionary 4
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