a person who brings an action in a court of law
"The lawyer prepared her opening statement to address the complainant's initial allegations against the defendant."
The party that brings a civil lawsuit against another; the plaintiff.
"The court heard arguments from both sides, but the complainant insisted on pursuing damages for the breach of contract."
In plain English: A complainant is someone who makes an official complaint about something they think is wrong.
"The complainant described how she felt unfairly treated by her neighbor."
Usage: Use complainant to refer specifically to the person or entity initiating a civil lawsuit, distinguishing it from criminal cases where the term victim is more common. This noun functions as a formal synonym for plaintiff and should not be confused with someone merely expressing dissatisfaction in everyday conversation.
The word comes from Old French complaignant, the present participle of complaindre. It entered English with its current meaning as a person who makes a formal complaint or brings an accusation against someone.