Excuse for gift given to prisoner (11)
I believe the answer is:
'excuse' is the definition.
'gift given to prisoner' is the wordplay.
'gift' becomes 'donation' (donation is a kind of gift).
'given to' means one lot of letters go next to another.
'prisoner' becomes 'con' (abbreviation for 'convict').
'donation' after 'con' is 'CONDONATION'.
'for' acts as a link.