Quarter of a circle (8)
I believe the answer is:
quadrant
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">quarter of a circle</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 quadrant that I've seen before include "One fourth of circle" , "Quarter-circle" , "Quarter of a circle or of its circumference" , "Quarter sector of circle" , "Half of a semicircle" .)