COMPLAINANT
plaintiff, complainant
(noun) a person who brings an action in a court of law
Source: WordNet® 3.1
Etymology
Noun
complainant (plural complainants)
(legal) The party that brings a civil lawsuit against another; the plaintiff.
(legal) An alleged victim in a criminal investigation or trial.
One who makes complaint.
Source: Wiktionary
Com*plain"ant, n. Etym: [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: Webster’s Unabridged Dictionary 1913 Edition