One who works with a will (8)
I believe the answer is:
executor
'one who works with a will' is the definition.
(an executor executes a deceased person's will)
This is the entire clue.
(Other definitions for executor that I've seen before include "Person who carries out the provisions of a will" , "Person appointed to carry out the terms of a will" , "One ensures terms of a will are carried out" , "Person nominated to carry out the terms of a will" , "One is appointed to carry out the terms of a will" .)