Worked to improve deli (6)
I believe the answer is:
toiled
'worked' is the definition.
(toiling is a kind of working)
'to improve deli' is the wordplay.
'improve' is an anagram indicator.
'deli' anagrammed gives 'iled'.
'to'+'iled'='TOILED'
(Other definitions for toiled that I've seen before include "Laboued long and hard" , "Worked laboriously and long" , "Worked long and hard" , "Worked or laboured very hard" , "Worked incessantly" .)