arbiter

2. N-COUNT : usu N of n

An arbiter of taste or style is someone who has a lot of influence in deciding what is fashionable or socially desirable.[ FORMAL ]

... Cobuild

Synonyms: judge, arbitrator, arbiter, referee, umpire

These nouns denote persons who make decisions that determine or settle points at issue. 

• A judge is one capable of making rational, dispassionate, and wise decisions:
  ... In this case, the jury members are the judges of the truth. 
• An arbitrator is either appointed or derives authority from the consent of the disputants:
  ... An experienced arbitrator mediated the contract dispute. 
• An arbiter is one whose opinion or judgment is recognized as being unassailable or binding:
  ... The critic considered himself an arbiter of fine literature. 
• A referee is an attorney appointed by a court to investigate and report on a case: 
  ... The referee handled many bankruptcy cases each month. 
• An umpire is a person appointed to settle an issue that arbitrators are unable to resolve:
  ... The umpire studied complex tax cases. 
  
  In sports referee and umpire refer to officials who enforce the rules and settle points at issue.

... Am-Heritage