arbiter

noun

Definitions of arbiter

an impartial (=not supporting or biased towards either of the disputing parties) person or institution given the power to decide in a dispute

They can leave questions of law to the decision of a tribunal, but they cannot make it the final arbiter on a question of law.

someone whose opinions about a subject influence people's beliefs and behaviour

The group eventually became the arbiters of the county's taste and public behaviour.