Creating a masterly monarch (6)
I believe the answer is:
making
'creating' is the definition.
('make' can be a synonym of 'create')
'a masterly monarch' is the wordplay.
'a masterly' becomes 'ma' (I can't justify this - if you can you should believe this answer much more).
'monarch' becomes 'king' (king is a kind of monarch).
'ma'+'king'='MAKING'
Can you help me to learn more?
(Other definitions for making that I've seen before include "production" , "Creating" , "Manufacturing" , "Fabricating" .)