Complain/kəmˈpleɪn/ Definition 1 of 3Pro Tip 1/3Express Discontent Use 'complain' to express unhappiness or dissatisfaction with a service or situation. She complained about the cold room at the hotel. Pro Tip 2/3Casual Expression 'Complain' is casual, suitable for everyday conversation when discussing minor annoyances. He always complains about the morning traffic. Pro Tip 3/3Polite Complaints To be polite, soften your complaint with phrases like 'I’m sorry to complain, but...'. I’m sorry to complain, but this coffee is cold.