Is a substitute to tolerate wrongdoing? (6,2)
I believe the answer is:
stands in
'is a substitute' is the definition.
'tolerate wrongdoing?' is the wordplay.
'tolerate' becomes 'stand' (synonyms).
'wrongdoing?' becomes 'sin' (sin is a kind of wrongdoing).
'stand'+'sin'='STANDS IN'
'to' acts as a link.
(Other definitions for stands in that I've seen before include "Acts as a substitute" , "acts for the moment" , "Deputises" , "deputy" , "Substitutes" .)