Excessive labour (7)
I believe the answer is:
travail
'excessive labour' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for travail that I've seen before include "Labour, toil" , "Exertion, elbow grease" , "Painful or laborious effort, like childbirth" , "Use of physical or mental energy; excessive labour..." , "Hard labour" .)