Acknowledged a deadly sin (6)
I believe the answer is:
agreed
'acknowledged' is the definition.
(eg acknowledged a point)
'a deadly sin' is the wordplay.
'deadly sin' becomes 'greed' (greed is a kind of deadly sin).
'a'+'greed'='AGREED'
(Other definitions for agreed that I've seen before include "admitted" , "Let's do it!" , "matched" , "Concurred - tallied" , "Saw eye to eye" .)