Respectful address: thưa + title

Thưa before a title opens what you say with respect, a little like "Sir" or "Madam": Thưa cô, em có câu hỏi. Excuse me, I have a question (a student to a woman teacher). It goes at the start, followed by the title or address word and a comma. Often dạ or your own word comes first: Dạ thưa cô, … Em thưa cô, em có câu hỏi.

You'll hear it where respect is expected: students to teachers (thưa thầy, thưa cô), patients to doctors (thưa bác sĩ), and in meetings, speeches and the news. After thưa, the same title usually stands for "you" in the rest of the sentence: Thưa thầy, thầy có rảnh không ạ?

A speech or a formal announcement opens with kính thưa and the audience: Kính thưa quý vị, ladies and gentlemen.

It's formal. With friends or at the market, people use the address word on its own, with dạ or ơi. Some families keep it at home: children say Thưa ba mẹ, con đi học when they leave for school. To get a waiter's attention, call Em ơi! (or Anh ơi! / Chị ơi! if they look older than you), not thưa.