Wherein to hide many a pain? (5)
I believe the answer is:
cache
'wherein to hide' is the definition.
I can't judge whether this defines the answer.
'many a pain?' is the wordplay.
'many' becomes 'c' (C is the Roman numeral for 100).
'a pain?' becomes 'ache' (ache is a kind of pain).
'c'+'ache'='CACHE'
Can you help me to learn more?
(Other definitions for cache that I've seen before include "Nest egg" , "Hiding place for treasure or store" , "Secretly keep" , "Hiding-place for treasure etc" , "Conceal" .)