Averse to one praying to cast off M&S clothing (4)
I believe the answer is:
anti
'averse to' is the definition.
I don't understand the rest of the clue.
(Other definitions for anti that I've seen before include "Opposition member" , "An opponent - opposed to party policy, etc" , "Who pooh-poohs all" , "One who is against (something)" , "Hostile" .)