Consented not to start vice (5)
I believe the answer is:
greed
'vice' is the definition.
(I've seen this before)
'consented not to start' is the wordplay.
'consented' becomes 'agreed' (agreeing is a kind of consenting).
'not to start' means to remove the first letter.
'agreed' with its first letter removed is 'GREED'.
(Other definitions for greed that I've seen before include "Eager desire" , "selfish habit" , "Avidity" , "Rapacity" , "Avarice, cupidity" .)