1 [sing] used as a polite way of speaking to a man whose name you do not know, for example in a shop or restaurant, or to show respect 先生（对男士的礼貌称呼，尤用于招呼顾客或表示尊敬）: I'm afraid we haven't got your size, sir. 对不起，先生，我们恐怕没有你的尺码。 ☞Look at madam. 参看madam。

2 [C] used at the beginning of a formal letter to a male person or male people （用于正式信函的开头，以称呼不知姓名的男士）: Dear Sir... 敬启者Dear Sirs... 敬启者 ☞Look at Madam. 参看Madam。

3 /sə(r) ||; sɚ/ [sing] the title that is used in front of the name of a man who has received one of the highest British honours （获颁英国最高荣誉者的称号）爵士