sir 
/ˈsɚ/ noun
plural sirs /ˈsɚ/ noun 1 [noncount] a — used without a name as a form of polite address to a man you do not know ▪ May I help you, sir? ▪ Sir, your order is ready. — compare ma'am, madam, miss
b — used without a name as a form of polite address to a man of rank or authority (such as a military or police officer, teacher, or master) ▪ “At ease, lieutenant.” “Yes sir, captain.” ▪ Sir, I don't think I was speeding. ▪ Sir, can you help me with this math problem? ▪ Dinner is ready, sir. 2 Sir [count] — used without a name as a form of address at the beginning of a formal letter ▪ Dear Sir or Madam ▪ Dear Sir/Sirs 3 Sir [noncount] — used as a title before the name of a knight or baronet ▪ Sir Lancelot ▪ Sir Charles ▪ Sir Elton John ▪ Sir Walter Scott 4 [noncount] US, informal — used in the phrases no sir and yes sir for emphasis, to show surprise, etc. ▪ I will not have that man in my home, no sir. [=no sirree] ▪ That was a wonderful dinner. Yes sir. [=yes sirree] ▪ “She couldn't have said that to her mom.” “Yes sir, she sure did.” ▪ “The teacher caught them kissing.” “No sir! She did?”
b — used without a name as a form of polite address to a man of rank or authority (such as a military or police officer, teacher, or master) ▪ “At ease, lieutenant.” “Yes sir, captain.” ▪ Sir, I don't think I was speeding. ▪ Sir, can you help me with this math problem? ▪ Dinner is ready, sir.
