Forgive crack by a bishop (7)
I believe the answer is:
absolve
'forgive' is the definition.
(I know that absolve is a more specific form of forgive)
'crack by a bishop' is the wordplay.
'crack' becomes 'solve' (crack can mean to solve or decipher).
'by' means one lot of letters go next to another.
'bishop' becomes 'B' (chess abbreviation).
'a'+'b'='ab'
'solve' after 'ab' is 'ABSOLVE'.
(Other definitions for absolve that I've seen before include "Discharge" , "Let off the hook" , "Free (a person) from guilt" , "Fully pardon" , "Clear of blame or quilt" .)