Learner's definition of COMPLAIN
to say or write that you are unhappy, sick, uncomfortable, etc., or that you do not like something
He works hard but he never complains.
If you're unhappy with the service, you should complain to the manager.
— often + about or of
Customers are sure to complain about the price increase.
In her letters, she complains of loneliness. [=she says that she is lonely]
She complained of a sore throat. [=she said she had a sore throat]
“How are you feeling?” “I can't complain.” [=I am not unhappy or ill; I am fine]
to say (something that expresses annoyance or unhappiness)