Single circuit (3)
I believe the answer is:
lap
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">single circuit</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for lap that I've seen before include "400 metres, typically" , "One round of the course" , "Circuit of racetrack" , "A circuit of a racecourse" , "Thighs, when seated" .)