An umpire or arbiter or judge (Job 9:33). This word is formed from the Latin diem dicere, i.e., to fix a day for hearing a cause. Such an one is empowered by mutual consent to decide the cause, and to "lay his hand", i.e., to impose his authority, on both, and enforce his sentence.

Noah Webster's New International Dictionary of the English Language

(n.) An umpire or arbiter; a mediator.