0 used as a formal and polite way of speaking to a man, especially one who you are providing a service to or who is in a position of authority:
1 used as the title of a knight (= a man who has been given a rank of honour by a British king or queen), with a first name or with both first and family names, but never with just the family name:
Sir Walter (Scott)
3 ( also Sir)used as a title with the first or full name of a man given a rank of honor by a king or queen
4 a formal and polite way of speaking to a man:
May I help you, Sir?
5 the usual way of beginning a formal letter to a man whose name you do not know:
Yes, sir; it has been thought that another method can be substituted for the portfolios: the men will have a book given them.
Surely that is a point that you can address, sir.
I am writing to ask if you, sir, can assist me to get the tenancy which was assigned to me.
Why is it, sir, that the 10-minute rule comes into force only at 6 pm?
My dear sir, it would be an excellent substitute for a sleeping draught.
No, sir; the reply to that part of the question is in the negative.
Yes sir; so far as the official information is concerned, it is correct.
There must be someone in the background, sir; it can't be the cousin.