sir · noun /sɜr/
sir
B1 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
Dictionary examples:
Would you like to see the menu, sir?
"Did you hear what I said?" "Yes, sir."
Learner example:
Suddenly, the man with the hat, sunglasses, and mask came to me and sa[id] "sir, what is your name?" (Preliminary English Test; B1; Thai)
Dear Sir
B2 a way of beginning a formal letter to a man whose name you do not know
Dictionary example:
Dear Sir, I am writing to...
Learner example:
Dear Sir or Madam, With reference to your advertisement in the Wall Street Journal [...] (First Certificate in English; B2; Spanish)
