Do laps in a pool (4)
I believe the answer is:
swim
'do laps in a pool' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for swim that I've seen before include "Take a dip" , "Do crawl, perhaps" , "Go for a dip" , "Crawl, say" , "At . . . . Two Birds by Flann O'Brien" .)