A turn's a bit of work for him (5)
I believe the answer is:
actor
'a turn's a bit of work for him' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'work for him' is the wordplay.
'work' becomes 'act' (synonyms).
'for him' becomes 'or' (I can't explain this - if you can you should give a lot more credence to this answer).
'act'+'or'='ACTOR'
Can you help me to learn more?
(Other definitions for actor that I've seen before include "eg Anthony Hopkins" , "Player - performer" , "Performer in drama" , "I pretend" , "Person performing on stage or screen" .)