Accept it's almost a sin (5)
I believe the answer is:
agree
'accept' is the definition.
(agreeing is a kind of accepting)
'almost a sin' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'sin' becomes 'greed' (greed is a kind of sin).
'a'+'greed'='agreed'
'agreed' with its last letter taken off is 'AGREE'.
'it's' is the link.
(Other definitions for agree that I've seen before include "See eye to eye" , "share the same view" , "Consent required" , "Square" , "Hold the same view" .)