"arbiter" in the noun sense
1. arbiter, supreme authority
someone with the power to settle matters at will
"she was the final arbiter on all matters of fashion"
2. arbiter, arbitrator, umpire
someone chosen to judge and decide a disputed issue
"the critic was considered to be an arbiter of modern literature"
"the arbitrator's authority derived from the consent of the disputants"
"an umpire was appointed to settle the tax case"
Source: WordNet® (An amazing lexical database of English)
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