Group of three notes (7)
I believe the answer is:
triplet
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">group of three notes</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for triplet that I've seen before include "One of a group of three" , "One of three born together" , "Group of three equal notes" , "One of three at the same birth" , "sibling?" .)