100 hurt in store (5)
I believe the answer is:
cache
'store' is the definition.
(cache is a kind of store)
'100 hurt' is the wordplay.
'a00' becomes 'c' ('C' can be a synonym of 'a00').
'hurt' becomes 'ache' ('ache' can be a synonym of 'hurt'**).
'c'+'ache'='CACHE'
'in' is the link.
(Other definitions for cache that I've seen before include "Hidden store of things" , "Reserve" , "Hiding place for treasure or stores" , "Conceal" , "Something hidden" .)