Enjoyment by day results in pay (4)
I believe the answer is:
fund
'pay' is the definition.
(thesaurus)
'enjoyment by day' is the wordplay.
'enjoyment' becomes 'fun' (I've seen this in another clue).
'by' means one lot of letters go next to another.
'day' becomes 'd' (abbreviation for day).
'fun'+'d'='FUND'
'results in' acts as a link.
(Other definitions for fund that I've seen before include "Pool - float" , "Stock of money available for particular purpose" , "Supply cash" , "Large stock; pay for" , "Reserve of money set aside for a purpose" .)