The Collaborative International Dictionary of English v.0.48:

Postman \Post"man\, n.; pl. Postmen.
   1. A post or courier; a letter carrier.
      [1913 Webster]

   2. (Eng. Law) One of the two most experienced barristers in
      the Court of Exchequer, who have precedence in motions; --
      so called from the place where he sits. The other of the
      two is called the tubman. --Whishaw.
      [1913 Webster]

WordNet (r) 3.0 (2006):

postman
    n 1: a man who delivers the mail [syn: mailman, postman,
         mail carrier, letter carrier, carrier]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

POSTMAN, Eng. law. A barrister in the court of exchequer, who has precedence
in: motions.