complainant

from WordNet (r) 3.0 (2006)

complainant
    n 1: a person who brings an action in a court of law [syn:
         {plaintiff}, {complainant}] [ant: {defendant}, {suspect}]

from The Collaborative International Dictionary of English v.0.48

Complainant \Com*plain"ant\ (k[o^]m*pl[=a]n"ant), n. [F.
   complaignant, p. pr. of complaindre.]
   1. One who makes complaint.
      [1913 Webster]

            Eager complainants of the dispute.    --Collier.
      [1913 Webster]

   2. (Law)
      (a) One who commences a legal process by a complaint.
      (b) The party suing in equity, answering to the plaintiff
          at common law.
          [1913 Webster]

                He shall forfeit one moiety to the use of the
                town, and the other moiety to the use of the
                complainant.                      --Statutes of
                                                  Mass.
          [1913 Webster]

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

COMPLAINANT. One who makes a complaint. A plaintiff in a suit in chancery is 
so called.

from Moby Thesaurus II by Grady Ward, 1.0

40 Moby Thesaurus words for "complainant":
      accusant, accuser, allegator, appellant, bellyacher, claimant,
      complainer, crab, crank, croaker, delator, faultfinder, frondeur,
      griper, grouch, grouser, growler, grumbler, impeacher, impugner,
      indictor, informer, kicker, kvetch, libelant, malcontent, murmurer,
      mutterer, party, petitioner, plaintiff, prosecutor,
      querulous person, reactionary, reactionist, rebel, sorehead,
      suitor, the prosecution, whiner