The Collaborative International Dictionary of English v.0.48:

Pleader \Plead"er\, n. [F. plaideur.]
   1. One who pleads; one who argues for or against; an
      advotate.
      [1913 Webster]

            So fair a pleader any cause may gain. --Dryden.
      [1913 Webster]

   2. (Law) One who draws up or forms pleas; the draughtsman of
      pleas or pleadings in the widest sense; as, a special
      pleader.
      [1913 Webster]

WordNet (r) 3.0 (2006):

pleader
    n 1: a lawyer who pleads cases in court [syn: advocate,
         counsel, counselor, counsellor, counselor-at-law,
         pleader]

Moby Thesaurus II by Grady Ward, 1.0:

86 Moby Thesaurus words for "pleader":
   abettor, actuator, advocate, agent, alter ego, alternate,
   amicus curiae, animator, apologete, apologist, apologizer,
   attorney, attorney-at-law, backup, backup man, barrister,
   barrister-at-law, cajoler, champion, coax, coaxer, counsel,
   counselor, counselor-at-law, defender, deputy, dummy, encourager,
   energizer, executive officer, exponent, figurehead, firer,
   friend at court, gadfly, galvanizer, impeller, inducer, inspirer,
   intercessor, justifier, lawyer, legal adviser, legal counselor,
   legal expert, legal practitioner, legalist, lieutenant, locum,
   locum tenens, mouthpiece, mover, moving spirit, paranymph,
   persuader, pinch hitter, prime mover, proctor, procurator,
   prompter, proponent, proxy, representative, sea lawyer,
   second in command, secondary, self-styled lawyer, solicitor, spark,
   spark plug, sparker, stand-in, stimulator, substitute,
   successful advocate, surrogate, tempter, understudy, utility man,
   vicar, vicar general, vice, vicegerent, vindicator, wheedler,
   whitewasher