Laboured (6)
I believe the answer is:
toiled
'laboured' is the definition.
('toil' can be a synonym of 'labour')
This is all the clue.
(Other definitions for toiled that I've seen before include "Worked incessantly" , "Struggled long and hard" , "Worked long and hard" , "Worked or laboured very hard" , "Worked laboriously and long" .)