Greed is a sin overwhelming all rogues initially (7)
I believe the answer is:
avarice
'greed' is the definition.
(synonyms)
'a sin overwhelming all rogues initially' is the wordplay.
'sin' becomes 'vice' ().
'overwhelming' means one lot of letters goes inside another.
'initially' indicates taking the first letters.
The first letters of 'all rogues' is 'ar'.
'vice' enclosing 'ar' is 'varice'.
'a'+'varice'='AVARICE'
'is' acts as a link.
(Other definitions for avarice that I've seen before include "Eager desire" , "One of seven deadly sins" , "Insatiable desire for wealth" , "Stinginess" , "Sway, control" .)