What is Complain ?
Complain is (verb) to say that something is no good or does not work properly (formal.) The shop is so cold the staff have started complaining. She complained about the service. They are complaining that our prices are too high. She complained that no one spoke English in the hotel. (NOTE: You complain to someone about something or that something is no good.)
source: Easier English, Student Dictionary Upper Intermediate Level