Cleric involved in secret sin immediately shown up (8)
I believe the answer is:
minister
'cleric' is the definition.
(thesaurus)
'involved in secret sin immediately shown up' is the wordplay.
'involved in' indicates a hidden word.
'shown up' says the letters should be written backwards.
'retsinim' is hidden within 'secret sin immediately'.
'retsinim' written backwards gives 'MINISTER'.
(Other definitions for minister that I've seen before include "Senior politician" , "supply as before" , "Clergyman - politician" , "Churchman" , "Clergyman - government member" .)