Arbiter, a Roman umpire, chosen by an agreement (in the Roman law compromissum) between contending parties, to decide their differences. His decision was called the arbi-trium. Such a judge, chosen by the parties themselves, was an arbiter receptus. An arbiter datus was appointed by the praetor to decide in matters purely of equity, while the judex decided in matters of law and precedent. The duties and rights of these officers, with the extent to which the decisions of an arbiter could be enforced, were sharply defined by the Roman law.