Relish swim (3)
I believe the answer is:
dip
I believe this clue is a double definition.
'relish' is the first definition.
(both can refer to a sauce for dipping food into)
'swim' is the second definition.
(dip is a kind of swim)
(Other definitions for dip that I've seen before include "Informally a short bathe" , "Sink; brief swim" , "Sudden sharp decrease in quantity" , "Pickpocket's" , "Decline" .)