Exist to turn to create immorality (4)
I believe the answer is:
evil
'immorality' is the definition.
(synonyms)
'exist to turn' is the wordplay.
'exist' becomes 'live' (synonyms).
'to turn' is a reversal indicator.
'live' back-to-front is 'EVIL'.
'to create' acts as a link.
(Other definitions for evil that I've seen before include "Maleficent" , "Extremely unpleasant" , "Morally corrupt" , "Wicked or immoral" , "Morally bad" .)