Sir
来自Big Physics
Middle English: reduced form of sire.
wiktionary
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, senior, señor, signor, and sire.
etymonline
sir
c. 1300, title of honor of a knight or baronet (until 17c. also a title of priests), variant of sire, originally used only in unstressed position. Generalized as a respectful form of address by mid-14c.; used as a salutation at the beginning of letters from early 15c. Not an acronym of anything.
