Source : Webster's Revised Unabridged Dictionary (1913)

Complainant \Com*plain"ant\, n. [F. complaignant, p. pr. of
   complaindre.]
   1. One who makes complaint.

            Eager complainants of the dispute.    --Collier.

   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.

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

Source : WordNet®

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