The Collaborative International Dictionary of English v.0.48:

Alderman \Al"der*man\ ([add]l"d[~e]r*man), n.; pl. Aldermen.
   [AS. aldormon, ealdorman; ealdor an elder + man. See Elder,
   n.]
   1. A senior or superior; a person of rank or dignity. [Obs.]
      [1913 Webster]

   Note: The title was applied, among the Anglo-Saxons, to
         princes, dukes, earls, senators, and presiding
         magistrates; also to archbishops and bishops, implying
         superior wisdom or authority. Thus Ethelstan, duke of
         the East-Anglians, was called Alderman of all England;
         and there were aldermen of cities, counties, and
         castles, who had jurisdiction within their respective
         districts.
         [1913 Webster]

   3. One of a board or body of municipal officers next in order
      to the mayor and having a legislative function. They may,
      in some cases, individually exercise some magisterial and
      administrative functions.
      [1913 Webster]