Sin of a vicar going wrong with end of service (7)
I believe the answer is:
avarice
'sin' is the definition.
(avarice is a kind of sin)
'a vicar going wrong with end of service' is the wordplay.
'going wrong with' indicates an anagram.
'end of' says to take the final letters.
The last letter of 'service' is 'e'.
'vicar' mixed up with 'e' makes 'varice'.
'a'+'varice'='AVARICE'
'of' acts as a link.
(Other definitions for avarice that I've seen before include "Cupidity" , "Greed - caviare (anag)" , "excessive desire for wealth" , "Wanting to be rich" , "Insatiable lust" .)