It's normal to be put off a wicked act (6,3)
I believe the answer is:
mortal sin
'a wicked act' is the definition.
'mortal sin' can be an answer for 'act' (mortal sin is a kind of act). I'm not sure about the 'a wicked' bit.
'it's normal to be put off' is the wordplay.
'to be put off' is an anagram indicator.
'its'+'normal'='itsnormal'
'itsnormal' is an anagram of 'MORTAL SIN'.
Can you help me to learn more?
(Other definitions for mortal sin that I've seen before include "heinous act" , "It causes the death of the soul - not venial" .)