A judicial or administrative magistrate. Originally the word was synonymous with “elder,” but was also used to designate an earl, and even a king. In English, law. An associate. to the chief civil magistrate of a corporate town or city. In American cities. The aldermen are generally a legislative body, having limited judicial powers as a body, as in matters of internal police regulation, laying out and repairing streets, constructing sewers, and the like; though in many cities they hold separate courts, and have magisterial powers to a considerable extent. Bouvier.