Three-sided figure (8)
I believe the answer is:
triangle
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">three-sided figure</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 triangle that I've seen before include "Polygon, could be isosceles" , "kitchen item" , "Percussion instrument of geometric origin" , "Geometrical figure - musical instrument" , "diamond cut in half?" .)