📒 used as a polite way of addressing a man whose name you do not know, for example in a shop or restaurant
📒 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
📒 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
📒 used as a form of address to a man in a position of authority, especially in the armed forces
📒 used as a form of address by children in school to a male teacher
📒 certainly not
📒 used to emphasize that something is true