Kitty's enjoyable day (4)
I believe the answer is:
fund
'kitty's' is the definition.
(fund or money for a particular purpose)
'enjoyable day' is the wordplay.
'enjoyable' becomes 'fun' (I've seen this in another clue).
'day' becomes 'd' (abbreviation for day).
'fun'+'d'='FUND'
(Other definitions for fund that I've seen before include "Pay for; kitty" , "Cash reserve" , "Pool of money" , "Stock, resources" , "Monetary resources" .)