Portion of a circle (3)
I believe the answer is:
arc
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">portion of a circle</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 arc that I've seen before include "Segment of circumference" , "Crescent" , "Turn" , "Curve of car" , "Part of a circular line" .)