Coven vying with deadly sin (4)
I believe the answer is:
'deadly sin' is the definition.
(envy is a kind of deadly sin)
'coven vying with' is the wordplay.
'with' says the answer is hidden in the clue.
'ENVY' is hidden within 'coven vying'.
(Other definitions for envy that I've seen before include "Covet; be jealous of", "Jealous feeling", "Desire of another's property etc", "Jealousy, resentment", "One of seven deadly sins".)