Once around a racetrack (3)
I believe the answer is:
lap
'once around a racetrack' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for lap that I've seen before include "Track circuit; drink" , "One circuit of track" , "A circuit of a racecourse" , "Round in a race" , "Circuit of racetrack" .)