Shop steward's back before priest (4)
I believe the answer is:
deli
'shop' is the definition.
(I've seen this before)
'steward's back before priest' is the wordplay.
'back' indicates one should take the final letters.
'before' is a charade indicator (letters next to each other).
'priest' becomes 'eli' (I've seen this before).
The last letter of 'steward' is 'd'.
'd'+'eli'='DELI'
(Other definitions for deli that I've seen before include "place to buy food" , "Specialised food shop" , "Special shop" , "Specialist foodshop(abbr.)" , "Fine food shop" .)