Calm debate has father overruling copper (10)
I believe the answer is:
dispassion
'calm' is the definition.
(thesaurus)
'debate has father overruling copper' is the wordplay.
I cannot really understand how this works, but
'father' could be 'pa' (pa can mean dad or father) and 'pa' is found in the answer.
'copper' could be 'di' (detective inspector, type of copper) and 'di' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for dispassion that I've seen is " detachment".)