/ ˈɑːbɪtə(r); NAmE ˈɑːrb-/ noun
arbiter (of sth) a person with the power or influence to make judgements and decide what will be done or accepted :
The law is the final arbiter of what is considered obscene.
an arbiter of taste / style / fashion
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WORD ORIGIN
late Middle English : from Latin , judge, supreme ruler .