What does “Mrs.” stand for?

Dear Straight Dope: My German in-laws stopped me cold with this question. Why is “missus” abbreviated as “Mrs.”? Where the hell does the “R” come from? My father-in-law, with his Hun self assurance, is convinced it has something to do with “mistress.” I think it’s a load of Kuhfladen but I have no response. What say you? Berkersheim Boy

Mac replies:

Better listen to your Hun father-in-law, son. Mrs. is an abbreviation for “mistress,” the feminine form of “mister,” which in turn originally meant “master.” Over time, the pronunciation of the married title slurred, and the term came to mean “paramour” or “kept woman” when pronounced in full. At that point, respectable married women ceased to ever spell out the title, and it has existed as a mumbled abbreviation ever since.

Mac

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What does “Mrs.” stand for?

A STAFF REPORT FROM THE STRAIGHT DOPE SCIENCE ADVISORY BOARD