Former copper starts to set everyone free (6)
I believe the answer is:
excuse
'free' is the definition.
(excusing is a kind of freeing)
'former copper starts to set everyone' is the wordplay.
'former' becomes 'ex' (prefix meaning former or onetime).
'copper' becomes 'cu' (Cu is the chemical symbol for copper).
'starts to' says to take the initial letters.
The initial letters of 'set everyone' is 'se'.
'ex'+'cu'+'se'='EXCUSE'
(Other definitions for excuse that I've seen before include "Defence of offensive behaviour" , "Forgive - allow to pass - plea" , "Grant an exemption or justify" , "Mitigate; forgive" , "Forgive or overlook an offence" .)