Shoe sale’s opening with everything reduced (6)
I believe the answer is:
sandal
'shoe' is the definition.
(sandal is a kind of shoe)
'sale's opening with everything reduced' is the wordplay.
'opening' suggests taking the first letters.
'with' becomes 'and'.
'everything' becomes 'all' (all things).
'reduced' means to remove the last letter.
The first letter of 'sales' is 's'.
'all' with its final letter removed is 'al'.
's'+'and'+'al'='SANDAL'
(Other definitions for sandal that I've seen before include "Item of footwear" , "Casual footwear" , "Light open-toed shoe" , "what may be afoot" , "Light footwear" .)