Entertain king, say, with beer (6)
I believe the answer is:
regale
'entertain' is the definition.
(I've seen this before)
'king say with beer' is the wordplay.
'king' becomes 'R' (abbreviation for rex, king in Latin).
'say' becomes 'eg' (both can mean for example).
'with' means one lot of letters go next to another.
'beer' becomes 'ale' (type of beer).
'r'+'eg'+'ale'='REGALE'
(Other definitions for regale that I've seen before include "Supply copiously" , "Fete" , "Generously entertain (with)" , "Amuse with stories" , "Entertain with conversation" .)