Definition of sir noun from the Oxford Advanced Learner's Dictionary

      

    sir

     noun
    noun
    BrE BrE//sɜː(r)//
     
    ; NAmE NAmE//sɜːr//
     
    ; BrE BrE//sə(r)//
     
    ; NAmE NAmE//sər//
     
     
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  1. 1  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 Good morning, sir. Can I help you? Are you ready to order, sir? ‘Report to me tomorrow, corporal!’ ‘Yes, sir!’ ‘Thank you very much.’ ‘You're welcome, sir. Have a nice day.’ compare ma’am see also madam
  2. 2  Dear Sir/Sirs 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 Dear Sir/Sirs Dear Sir or Madam
  3. 3  Sir 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 Sir Paul McCartney Thank you, Sir Paul. compare lady
  4. 4(British English) used as a form of address by children in school to a male teacher Please, sir, can I open a window? compare miss
  5. Word Origin Middle English: reduced form of sire.Idioms (informal, especially North American English) certainly not We will never allow that to happen! No sir! (informal, especially North American English) used to emphasize that something is true That's a fine car you have. Yes sir!
See the Oxford Advanced American Dictionary entry: sir