Fool entertaining king's demands (4)
I believe the answer is:
asks
'demands' is the definition.
('ask' can be a synonym of 'demand')
'fool entertaining king's' is the wordplay.
'fool' becomes 'ass' (ass is a kind of fool**).
'entertaining' is an insertion indicator.
'king' becomes 'k'.
'ass' enclosing 'k' is 'ASKS'.
(Other definitions for asks that I've seen before include "Poses a question" , "Demands (something of someone)" , "Inquires (4)" , "Makes an inquiry" , "Requests information about" .)