Sailor returned before the swim (5)
I believe the answer is:
bathe
'swim' is the definition.
(bathe is a kind of swim)
'sailor returned before the' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'returned' says the letters should be written in reverse.
'before' is a charade indicator (letters next to each other).
'ab' back-to-front is 'ba'.
'ba'+'the'='BATHE'
(Other definitions for bathe that I've seen before include "Immerse oneself in water" , "Wash, soak" , "Swim in sea" , "Suffuse" , "Steep" .)