The Collaborative International Dictionary of English v.0.48:

Champerty \Cham"per*ty\, n. [F. champart field rent, L.
   campipars; champ (L. campus) field + part (L. pars) share.]
   1. Partnership in power; equal share of authority. [Obs.]
      [1913 Webster]

            Beaut['e] ne sleighte, strengthe ne hardyness,
            Ne may with Venus holde champartye.   --Chaucer.
      [1913 Webster]

   2. (Law) The prosecution or defense of a suit, whether by
      furnishing money or personal services, by one who has no
      legitimate concern therein, in consideration of an
      agreement that he shall receive, in the event of success,
      a share of the matter in suit; maintenance with the
      addition of an agreement to divide the thing in suit. See
      Maintenance.
      [1913 Webster]

   Note: By many authorities champerty is defined as an
         agreement of this nature. From early times the offence
         of champerty has been forbidden and punishable.
         [1913 Webster]

WordNet (r) 3.0 (2006):

champerty
    n 1: an unethical agreement between an attorney and client that
         the attorney would sue and pay the costs of the client's
         suit in return for a portion of the damages awarded;
         "soliciting personal injury cases may constitute champerty"