Store clerks face pain (5)
I believe the answer is:
cache
'store' is the definition.
(I know that cache is a type of store)
'clerks face pain' is the wordplay.
'face' suggests taking the first letters.
'pain' becomes 'ache' (ache is a kind of pain).
The first letter of 'clerks' is 'c'.
'c'+'ache'='CACHE'
(Other definitions for cache that I've seen before include "Something hidden" , "Collection of hidden things" , "Hiding place for treasure or stores" , "Secret hiding place" , "Stockpile" .)