On crusade to get pardon (9)
I believe the answer is:
remission
'pardon' is the definition.
(remission is a kind of pardon)
'on crusade' is the wordplay.
'on' becomes 're' ('on' can be mean 'with reference to').
'crusade' becomes 'mission' (both can mean a campaign or goal).
're'+'mission'='REMISSION'
'to get' is the link.
(Other definitions for remission that I've seen before include "Forgiveness for sins for missioner" , "Relief" , "Lessening of a term of imprisonment" , "Cancellation (of a debt)" , "Reduction of sentence" .)