n.

1. 先生，阁下；老师；长官
   This way, sir.

   先生，这边请。

2. （大写）爵士
   Sir Walter Scott was a famous British writer.

   沃尔特·斯科特爵士是英国著名作家。

3. 【幽】（对被申斥者，孩子等的挖苦）老兄；“先生”
4. 【口】【幽】男教师，先生[E]

n.

1. a polite or respectful form of address to a man.
2. used to address a man at the beginning of a formal or business letter.
3. used as a title before the forename of a knight or baronet.