Other forms: complainants
In law, the person who accuses someone else of wrongdoing is sometimes called the complainant. You are the complainant if you sue your neighbor for building a chicken coop on your property.
Although there are some technical differences in the way legal experts use the terms, a complainant is essentially the same as a plaintiff. They're both ways to refer to an accuser, or someone bringing an official grievance against someone else. Since the 15th century, complainant has been used to mean "one who makes a formal complaint in court, " from complain.