sir

Etymology

From Middle English sir, unstressed form of sire, borrowed from Old French sire (“master, sir, lord”), from Latin senior (“older, elder”), from senex (“old”). Doublet of seigneur, seignior, senhor, senior, señor, signor, and sire.

noun

1. A man of a higher rank or position.
2. A respectful term of address to a man of higher rank or position
   1. to a knight or other low member of the peerage.
      Just be careful. He gets whingy now if you don't address him as Sir John.
   2. to a superior military officer.
      Sir, yes sir.
   3. to a teacher.
      Here's my report, sir.
3. A respectful term of address to an adult male (often older), especially if his name or proper title is unknown.
   Excuse me, sir, do you know the way to the art museum?

verb

1. To address (someone) using "sir".
   Sir, yes, sir! —Don't you sir me, private! I work for a living!
   Don't "Sir" me, young man, you have no idea who you're dealing with! 1997, Ed Solomon, Men in Black, spoken by Agent K (Tommy Lee Jones)