Simple percussion instrument (8)
I believe the answer is:
triangle
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">simple percussion instrument</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for triangle that I've seen before include "Figure - percussion instrument" , "Three-sided figure - musical instrument" , "Relating to percussion instrument" , "Constellation - three-sided figure" , "Three-sided polygon" .)