Arbitrators and arbiters are both types of judges but they act in different contexts.
       arbitrator (noun ): a neutral person either chosen by the parties to an arbitration agreement or by a court or arbitration institute to hear the parties' claims and render a decision. An arbitrator judges only in arbitration proceedings.
The sole arbitrator was appointed by the Chamber of Commerce.
       arbiter (noun ): an impartial (=not supporting or biased towards either of the disputing parties) person or institiution given the power to decide in a dispute.  An arbiter has the power to decide in any sort of controversy.
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.
       arbitration (noun ): the reference of a dispute to an impartial (third) person chosen by the parties who agree in advance to abide by the arbitration award issued after the hearing at which both parties have an opportunity to be heard. An arbitration proceeding is a form of alternative dispute resolution which is held outside of court.
The parties decided to refer the dispute to arbitration pursuant to the terms of their agreement.
       arbitrage (noun ): the simultaneous buying and selling of currencies or securities at two different prices in two different markets to profit from price discrepancies (=differences between two things that should be the same).
Index arbitrage and outright manipulation have come to dominate trading in some areas.
Source: Translegal

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