Mistake for each item of footwear (7)
I believe the answer is:
slipper
'item of footwear' is the definition.
(I've seen this before)
'mistake for each' is the wordplay.
'mistake' becomes 'slip' (slip is a kind of mistake**).
'for each' becomes 'per' (I've seen this before).
'slip'+'per'='SLIPPER'
(Other definitions for slipper that I've seen before include "Type of footwear" , "Casual footwear" , "Comfortable shoe" , "Beat; mule" , "Footwear item" .)