Shop's opening during consumer festival (6)
I believe the answer is:
easter
'festival' is the definition.
(Christian festival)
'shop's opening during consumer' is the wordplay.
'opening' says to take the initial letters.
'during' is an insertion indicator.
'consumer' becomes 'eater' (consume can mean to eat).
The initial letter of 'shops' is 's'.
's' placed inside 'eater' is 'EASTER'.
(Other definitions for easter that I've seen before include "Major Christian festival in April" , "Christian celebration for Teresa" , "A terse sort of Spring festival?" , "Snug retreat" , "Sort of tide" .)