A King stung by Queen's authority (7)
I believe the answer is:
arbiter
'authority' is the definition.
(thesaurus)
'a king stung by queen's' is the wordplay.
'a king' becomes 'ar' (I've seen this in other clues**).
'stung' becomes 'bit' ('bit' can be a synonym of 'stung').
'by' means one lot of letters go next to another.
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'ar'+'bit'+'er'='ARBITER'
(Other definitions for arbiter that I've seen before include "Source of authority" , "Judge - mediator" , "Rear bit (anag.)" , "Judge, umpire" , "Mediator or referee" .)