Source : Webster's Revised Unabridged Dictionary (1913)

Arches \Arch"es\,
   pl. of {Arch}, n.

   {Court of arches}, or {Arches Court} (Eng. Law), the court of
      appeal of the Archbishop of Canterbury, whereof the judge,
      who sits as deputy to the archbishop, is called the Dean
      of the Arches, because he anciently held his court in the
      church of St. Mary-le-Bow (de arcubus). It is now held in
      Westminster. --Mozley & W.