Evil Clergyman at last is back (3)
I believe the answer is:
sin
'evil' is the definition.
(thesaurus)
'clergyman at last is back' is the wordplay.
'at last' says to take the final letters.
'back' says the letters should be written backwards.
The final letter of 'clergyman' is 'n'.
'n'+'is'='nis'
'nis' written backwards gives 'SIN'.
(Other definitions for sin that I've seen before include "Trespass" , "Depravity" , "Evil" , "Transgression of moral law" , "It breaches the moral law" .)