Meaning

noun term of address for a man

noun a title used before the name of knight or baronet

originFrom 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, senyor, signore, and sire.

Etymology from Wiktionary, CC BY-SA 3.0