Hoard one hundred yen (5)
I believe the answer is:
cache
'hoard' is the definition.
('cache' can be a synonym of 'hoard')
'one hundred yen' is the wordplay.
'one hundred' becomes 'c' (Roman numeral).
'yen' becomes 'ache' ('ache' can be a synonym of 'yen').
'c'+'ache'='CACHE'
(Other definitions for cache that I've seen before include "Secret source" , "Hiding place for treasure or store" , "Reserve" , "Conceal" , "Hidden storage space" .)