noun A grievance, problem, difficulty, or concern.
I have no complaints about the quality of his work, but I don't enjoy his company.
noun In a civil action, the first pleading of the plaintiff setting out the facts on which the claim is based.
noun In criminal law, the preliminary charge or accusation made by one person against another to the appropriate court or officer, usually a magistrate.
noun A bodily disorder or disease; the symptom of such a disorder.
Don't come too close; I've got this nasty complaint.