Coppers welcoming an act of atonement (7)
I believe the answer is:
penance
'act of atonement' is the definition.
(I've seen this before)
'coppers welcoming an' is the wordplay.
'coppers' becomes 'pence' (coppers can mean copper coins).
'welcoming' is an insertion indicator (in sense of 'inviting in').
'pence' enclosing 'an' is 'PENANCE'.
(Other definitions for penance that I've seen before include "Act imposed for sin" , "Punishment inflicted on oneself" , "Voluntary self-abasement" , "Self-punishment for sin" , "Voluntary self-punishment" .)