Master game and finally steal queen (5)
I believe the answer is:
ruler
'master' is the definition.
(thesaurus)
'game and finally steal queen' is the wordplay.
'game' becomes 'ru' (rugby union).
'and' is a charade indicator (letters next to each other).
'finally' says to take the final letters.
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
The final letter of 'steal' is 'l'.
'ru'+'l'+'er'='RULER'
(Other definitions for ruler that I've seen before include "leader in government" , "Queen maybe" , "Queen, perhaps" , "King, president etc." , "Maharaja, e.g." .)