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English definition of “Sir”

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Sir

noun [S]
 
 
/sɜːr/ formal
a formal and polite way of speaking to a man: May I help you, Sir?
Dear Sir the usual way of beginning a formal letter to a man whose name you do not know: Dear Sir, I am writing to complain about the quality of the service I received last week.
Dear Sir or Madam used to begin a formal letter when you do not know whether the person you are writing to is a man or a woman: Dear Sir or Madam, I am writing to inform you that I wish to cancel my credit card.
Dear Sirs old-fashioned used to begin a letter to a company when you do not have someone's name to write to directly
→  Compare Madam
(Definition of Sir from the Cambridge Business English Dictionary © Cambridge University Press)
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