Lee returned as swimmer (3)
I believe the answer is:
eel
'swimmer' is the definition.
(eels swim)
'lee returned' is the wordplay.
'returned' says the letters should be written backwards.
'lee' back-to-front is 'EEL'.
'as' acts as a link.
(Other definitions for eel that I've seen before include "slipper" , "Slippery swimmer (may be jellied)" , "Slimy fish" , "A sea snake" , "Unagi, in a sushi bar" .)