1. The party who brings a legal complaint against another; esp., the plaintiff in a court of equity or, more modernly, a civil suit.
“A suit in equity, under the procedure of the English Court of Chancery, which was generally adopted in the American States prior to the code, is instituted by the plaintiff filing a bill of complaint. The plaintiff is usually called the complainant, in the Federal courts the complainant or plaintiff indifferently. The bill is in substance a petition to the chancellor, or judge of the court of equity, setting forth at large the grounds of the suit, and praying the process of the court, its subpoena, to bring the defendant into court and compel him to answer the plaintiff’s bill, and, also, for such relief by decree or interlocutory remedy, by way of injunction, etc., as the plaintiff supposes himself entitled to.” Edwin E. Bryant, The Law of Pleading Under the Codes of Civil Procedure 55 (2d ed. 1899).
2. A person who, under oath, signs a statement (called a “complaint”) establishing reasonable grounds to believe that some named person has committed a crime.
— Also termed affiant. [Cases: Criminal Law 210. C.J.S. Criminal Law § 326.]