The Etymology of Arbiter
Arbiter is one of those Latin words whose deeper etymology is delightfully fuzzy. The most-cited proposal derives it from ad- (to) + an obsolete verb baetere (to come, go), making the original sense one who comes to witness — a person summoned to a dispute as observer and judge. In Roman law arbiter had a precise meaning: a private judge chosen by both parties to a dispute, as distinct from a iudex (a public state-appointed judge). The arbiter's decision was binding because both sides had agreed to submit to it — hence English arbitration, the same root, for any voluntary submission to a third-party decider. English borrowed arbiter directly from Latin in the 1500s and kept the dignified sense of an authoritative judge. The phrase arbiter of taste or arbiter elegantiae preserves Petronius's ancient nickname: at Nero's court he was, formally, the man who decided what was fashionable.