Money, we hear, in hidden store (5)
I believe the answer is:
cache
'hidden store' is the definition.
(I've seen this before)
'money we hear' is the wordplay.
'money' becomes 'cash' (cash is a type of money).
'we hear' shows a homophone (sound like).
'cash' sounds like 'CACHE'.
'in' acts as a link.
(Other definitions for cache that I've seen before include "(Place in) hidden store" , "Hidden storage space" , "Hiding place for treasure or stores" , "what things could be stored in" , "Hiding-place for treasure etc" .)