Clear of secret corruption (4-4)
I believe the answer is:
scot-free
'clear' is the definition.
(thesaurus)
'of secret corruption' is the wordplay.
'corruption' indicates anagramming the letters.
'of'+'secret'='ofsecret'
'ofsecret' with letters rearranged gives 'SCOT-FREE'.
(Other definitions for scot-free that I've seen before include "'Without any punishment whatsoever (4,4)'" , "(Get off) without punishment" , "Secret of being unpunished - like Jock?" , "(Get away) incurring no penalty" , "See 12" .)