to say that you are not happy or satisfied with something or someone

That may be complained of.

simple past tense and past participle of complain

present participle of complain

The act by which someone complains; a complaint.

(law) The party that brings a civil lawsuit against another; the plaintiff. / (law) An alleged victim in a criminal investigation or trial. / One who makes complaint.

Third-person singular simple present indicative form of complain

One who complains, or is known for their complaints.

plural of complainer

plural of complaining