When in the money, an atonement (7)
I believe the answer is:
penance
'atonement' is the definition.
(I've seen this before)
'when in the money an' is the wordplay.
'when in' is an insertion indicator.
'the money' becomes 'pence' (I've seen this in other clues).
'pence' enclosing 'an' is 'PENANCE'.
(Other definitions for penance that I've seen before include "Self-imposed punishment" , "Punishment imposed for sin" , "sacrament" , "Act imposed for sin" , "Voluntary punishment to atone for sin" .)