Delightful day for Kitty (4)
I believe the answer is:
fund
'for kitty' is the definition.
(fund or money for a particular purpose)
'delightful day' is the wordplay.
'delightful' becomes 'fun' (I can't explain this - if you can you should give a lot more credence to this answer).
'day' becomes 'd' (abbreviation for day).
'fun'+'d'='FUND'
Can you help me to learn more?
(Other definitions for fund that I've seen before include "Pay for; kitty" , "Pool of money" , "Give money" , "Monetary resources" , "Cash reserve" .)