Coven vying with deadly sin (4)
I believe the answer is:
envy
'deadly sin' is the definition.
(envy is a kind of deadly sin)
'coven vying with' is the wordplay.
'with' indicates the answer is hidden within the clue.
'ENVY' can be found hidden inside 'coven vying'.
(Other definitions for envy that I've seen before include "Deadly sin; sounds like two letters" , "Desire as a rival" , "Jealous feeling" , "The green-eyed emotion" , "Jealous emotion - deadly sin" .)