(formerly) a loud cry (or repeated cries) of pain or rage or sorrow
"The doctor winced as she heard the patient's complaint echo through the hallway, his voice rising in agony after every injection."
an expression of grievance or resentment
"After waiting forty minutes for a table, she finally voiced her complaint about the restaurant's poor management to her friend."
(civil law) the first pleading of the plaintiff setting out the facts on which the claim for relief is based
"The attorney spent hours drafting the complaint to ensure every fact supporting our client's damages was clearly detailed."
The act of complaining.
"The constant complaint about the weather finally made everyone want to leave the porch."
In plain English: A complaint is when someone expresses that they are unhappy about something.
"She filed a formal complaint against the noisy neighbor."
Usage: A complaint is a formal expression of dissatisfaction or grievance regarding a specific issue, rather than the general feeling of being upset. Use it when referring to an official statement made to resolve a problem, such as filing a customer service complaint.
The word complaint entered English from the Old French compleindre, which originally meant "to lament" or "mourn." It is ultimately derived from the Latin planctus, referring to a cry of grief.