Mistake for every footwear item (7)
I believe the answer is:
slipper
'footwear item' is the definition.
(I've seen this before)
'mistake for every' is the wordplay.
'mistake' becomes 'slip' (slip is a kind of mistake**).
'for every' becomes 'per' (I've seen this before).
'slip'+'per'='SLIPPER'
(Other definitions for slipper that I've seen before include "Accident-prone" , "Indoor shoe" , "Casual footwear" , "Light shoe" , "Shoe worn indoors" .)