Claim: A choice cut of beef taken from the upper hindquarter (i.e., the loin) of a cow is called "sirloin" because an English king was once so delighted with his meal that he knighted the meat, dubbing it "Sir Loin."
Examples:
. . . should presently enter combat with a worthy knight, called Sir Loyne of Beefe, and overthrow him.1
Dining with the Abbot of Reading, [Henry VIII] ate so heartily of a loin of beef that the abbot said he would give 1,000 marks for such a stomach. "Done!" said the king, and kept the abbot a prisoner in the Tower, won his 1,000 marks, and knighted the beef.
[ . . .]
A Sir-loyne of beef was set before Him (so knighted, saith tradition, by this King Henry).2
[O]ur King James First, who loved good eating, being invited to Dinner by one of his Nobles, and seeing a large Loyn of Beef at his Table, he drew out his Sword, and in a frolic knighted it.3
This joint is said to owe its name to King Charles the Second, who dining upon a Loin of Beef, said for its merit it should be knighted, and henceforth called Sir-Loin.4
Origins: If we needed proof that inventing silly stories to explain the origins of words with non-obvious etymologies is both an old and long-lived practice, here
it is: Across nearly four centuries, various writers have chronicled the tale that an English king especially fond of fine dining (any one of a succession from Henry VIII to Charles II) coined the word "sirloin" by knighting a choice piece of meat, thereby introducing "Sir Loin" to the world. Even the venerable Samuel Johnson included the anecdote in his Dictionary of the English Language (1755), noting under the definition of the word "sir" that it was "A title given to the loin of beef, which one of our kings knighted in a fit of good humour."5
While it is certainly possible that one or more kings of England has repeated this pun, the joke cannot be the source of the word "sirloin," which appeared in English as far back as the mid-sixteenth century, antedating the ascension of any of the named kings (save Henry VIII) to the throne. More importantly, though, it was not until the eighteenth century that the word "sirloin" came to be commonly spelled with an "i" — until then it was generally written as "surloin," indicating that it came from the Middle French surlonge (sur meaning "over" and longe meaning "loin"), just as the word "surname" came from the same French root (sur), indicating a family name that was used "over" (i.e., in addition to) one's Christian name.
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