Pool entertaining duke (4)
I believe the answer is:
fund
'pool' is the definition.
(I've seen this before)
'entertaining duke' is the wordplay.
'entertaining' becomes 'fun' (similar in meaning).
'duke' becomes 'd' (abbreviation).
'fun'+'d'='FUND'
(Other definitions for fund that I've seen before include "Reserve of money for future use" , "Finance" , "Monetary resources" , "Sponsor" , "Capitalize" .)