Lap speed (4)
I believe the answer is:
lick
I believe this clue is a double definition.
'lap' is the first definition.
('lick' can be a synonym of 'lap')
'speed' is the second definition.
(I've seen this before)
(Other definitions for lick that I've seen before include "A - - and a promise" , "Moisten" , "Feel with the tongue" , "Eat with tongue" , "Defeat (informal) - speed (informal)" .)