Wantonly sins with zeal - not with this sin! (8)
I believe the answer is:
laziness
'this sin' is the definition.
(laziness is a kind of sin)
'wantonly sins with zeal not with' is the wordplay.
'wantonly' indicates an anagram (I've seen this in other clues).
'not' indicates named letters should be taken away.
'sins'+'with'+'zeal'='sinswithzeal'
'sinswithzeal' with 'with' taken away is 'sinszeal'.
'sinszeal' with letters rearranged gives 'LAZINESS'.
(Other definitions for laziness that I've seen before include "Idleness" , "Lethargy" , "Indolence, sloth" .)