He works with a will (8)
I believe the answer is:
executor
'he works with a will' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
This is the entire clue.
Can you help me to learn more?
(Other definitions for executor that I've seen before include "Administrator" , "Person who sees that a will is followed" , "Will enactor" , "One is appointed to carry out the terms of a will" , "One carries out the terms of a will" .)