noun

• A respectful term of address to a man of higher rank or position, particularly:
  "Jeeves: Foreign travel often liberates emotions best kept in check, sir. The air of North America is notoriously stimulating in this regard, as witness the regrettable behavior of its inhabitants in 1776. B. Wooster: Hm? What happened in 1776, Jeeves? Jeeves: I prefer not to dwell on it, if it's convenient to you, sir."
• A respectful term of address to a man of higher rank or position, particularly:
  "Just be careful. He gets whingy now if you don't address him as Sir John."
• A respectful term of address to a man of higher rank or position, particularly:
  "Sir, yes sir."
• A respectful term of address to a man of higher rank or position, particularly:
  "Here's my report, sir."

verb

• (transitive, informal) To address another individual using "sir".
  "Sir, yes, sir! —Don't you sir me, private! I work for a living!"

noun

• (British) The titular prefix given to a knight or baronet.
• (Philippines, colloquial or informal) A respectful term of address or reference to a man of higher rank or position before the man's given name or nickname.

noun

• (manufacturing) Initialism of surface insulation resistance.
• (biochemistry, genetics) Abbreviation of silent information regulator.