Worked hard (6)
I believe the answer is:
toiled
'worked hard' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for toiled that I've seen before include "Worked laboriously and long" , "Worked or laboured very hard" , "Worked long and hard" , "Struggled long and hard" , "Worked incessantly" .)