sir

1.（对不认识的男性的称呼或对男性的尊称）先生used as a polite way of addressing a man whose name you do not know, for example in a shop/store or restaurant, or to show respect

2. （正式信函中对不知其名的男性收信人的称呼）先生，阁下used at the beginning of a formal business letter when you do not know the name of the man or people that you are dealing with

3.（贵族头衔，用于爵士或准男爵的名字或姓名前面）爵士a title that is used before the first name of a man who has received one of the highest British honours (= a knight ), or before the first name of a baronet

4.（中小学生对男教师的称呼）先生，老师used as a form of address by children in school to a male teacher

1.先生,阁下,君

2.〈谑〉大人,先生

3.先生;各位,执事诸君

4.〈英〉爵士

5.〈谑〉喂,老兄

6.议长

7.〈美口〉不分性别,用以强调肯定或否定

1.称...为先生

1.used as a polite way of speaking to a man. This word can be used by someone who works in a store or restaurant for speaking to a customer, by someone speaking to a senior officer, or by someone speaking to another person whose name they do not know; used by a boy or young man as a polite way of speaking to an older man

2.used by students for talking to or about a male teacher

3.used before the name of a man who is a knight or baronet