Many long for hidden store (5)
I believe the answer is:
cache
'hidden store' is the definition.
(I've seen this before)
'many long' is the wordplay.
'many' becomes 'c' (C is the Roman numeral for 100).
'long' becomes 'ache' (to long for something is to ache for it).
'c'+'ache'='CACHE'
'for' is the link.
(Other definitions for cache that I've seen before include "Treasury" , "Hidden storage place" , "Concealed store" , "Hiding place for treasure or stores" , "Collection of hidden things" .)