Enjoyable day in store (4)
I believe the answer is:
fund
'store' is the definition.
(I know that store can be written as fund)
'enjoyable day' is the wordplay.
'enjoyable' becomes 'fun' (fun means enjoyable or pleasing).
'day' becomes 'd' (abbreviation for day).
'fun'+'d'='FUND'
'in' acts as a link.
(Other definitions for fund that I've seen before include "Pool of money" , "Large stock; pay for" , "Provide with money, say project" , "Cash reserve" , "Stock of money available for particular purpose" .)