Apology from former copper, with site vacated (6)
I believe the answer is:
excuse
'apology' is the definition.
(I've seen this before)
'former copper with site vacated' is the wordplay.
'former' becomes 'ex'.
'copper' becomes 'cu' (chemical symbol).
'with' is a charade indicator (letters next to each other).
'vacated' means to remove the middle letters.
'site' with its centre taken out is 'se'.
'ex'+'cu'+'se'='EXCUSE'
'from' acts as a link.
(Other definitions for excuse that I've seen before include "Mitigate; forgive" , "Let off; defence" , "Let off the hook" , "Grant exemption or release to" , "Release (from a duty)" .)