Criticise, or return a saint (5)
I believe the answer is:
roast
'criticise' is the definition.
(I've seen this before)
'or return a saint' is the wordplay.
'return' is a reversal indicator.
'saint' becomes 'st' (abbreviation).
'or' back-to-front is 'ro'.
'ro'+'a'+'st'='ROAST'
(Other definitions for roast that I've seen before include "Slate" , "Heat strongly - criticise excessively" , "Give a telling off to - cook" , "open-air party in US" , "Berate - cook" .)