Worked to return deli (6)
I believe the answer is:
toiled
'worked' is the definition.
(toiling is a kind of working)
'to return deli' is the wordplay.
'return' says the letters should be written backwards.
'deli' reversed gives 'iled'.
'to'+'iled'='TOILED'
(Other definitions for toiled that I've seen before include "Worked laboriously and long" , "Worked incessantly" , "Worked or laboured very hard" , "Laboued long and hard" , "Struggled long and hard" .)