Let us now put down our smartphones to mark a peculiar anniversary. One hundred years ago, on Sept. 9, 1917, a retired admiral of the British navy fired off a letter to Winston Churchill, the future prime minister. The letter was shockingly prescient in one curious way: the admiral abbreviated "Oh my God!” in a most millennial fashion, as "OMG.”….

In his letter, Lord Fisher complained to the much younger Churchill, then serving as minister of munitions, about Britain’s cautious naval strategy against Germany. In a sarcastic tone, he closed the letter by writing, "I hear that a new order of Knighthood is on the tapis—O.M.G. (Oh! My God!)—Shower it on the Admiralty!!” ("On the tapis” meant "under consideration.”)

Lord Fisher’s letter went unnoticed for nearly a century until it was unearthed by lexicographers at the Oxford English Dictionary, when they added an entry for "OMG” in March 2011. The OED makes a point of tracking down the earliest known example of every word or phrase, and initial research had taken the interjection "OMG” back to 1994, in an online forum for soap-opera fans ("OMG! What did it say?”).

The editors asked one of the OED’s longtime library researchers, Jon Simon, formerly a research librarian at the Library of Congress, to track down another mid-’90s example of "OMG” that cropped up in the Arkansas Democrat-Gazette. But Mr. Simon didn’t stop there: He looked carefully through the Google Books database of digitized texts until he found the surprising 1917 letter, included in Lord Fisher’s memoirs published two years later….