Americans have always been more certain about the origin of the word OK (if it is a word, rather than an abbreviation for two words) than the envious Brits: British dictionaries acknowledge that the most likely etymology is a comical misspelling of the phrase "all correct," and that this joke originated in the United States in the 19th century, but they are cautious about exactly where the first use was recorded.
Americans are much quicker to produce examples of the first use - they are understandably proud that this most common of all international words is an American export, perhaps the most powerful U.S. influence on global culture.
Allan Metcalf, the author of the recent book OK: The Improbable Story of America's Greatest Word, picks, as many historians do, one completely certain use from 1839 as the first recorded printed reference. He recounts in detail how the Boston Morning Post, as part of a 19th-century fad for abbreviations and initials, was fond of joking with deliberately incorrect ones ("OW," for example, stood for "all right" in its pages). It actually explained the new joke in a parenthesis: "o.k. (all correct)." The joke was repeated during a subsequent presidential election, because of the coincidence that one of the candidates was nicknamed Old Kinderhook.
Of course, this word and meaning may have been used in speech long before it cropped up in print. There are American handwritten letters and diary entries that contain the letters "ok" from as early as 1790, but whether they meant what we now mean is disputed.
Another popular theory about the origin of the word is that it is an anglicization of a word from an African language used by U.S. slaves. But that, too, is impossible to prove in the absence of written records. The fact that the native-American Choctaw word okeh means something like "it is so" is just a coincidence, Metcalf explains ( pace President Woodrow Wilson, who apparently signed documents with that word as an intellectual variation).
In fact, Metcalf devotes a whole chapter to the various false etymologies of OK, including several you may have heard (the Scots say " och aye" and in German " ohne Korrektur" means no correction needed), and then the far-fetched ones (the first timber laid in shipbuilding was marked for the Outer Keel; there is a port in Haiti called Aux Cayes that produced a popular rum).
It may well be that the Finnish word oikea means correct, but it's tough to explain how Finnish might have gained such a global reach. I once heard a French speaker claim that " aux quais" meant that something was ready to be picked up, therefore shipshape, and that English speakers must have bastardized this eminently useful phrase - demonstrating a familiar European denial of American influence.
Metcalf explains that the global success of this word comes partly from its easy sound: Almost every language in the world contains the vowel sounds o and ay and the consonant sound k. So it sounded familiar and travelled well, a virus whose national origin was invisible.
Another tough question is how to write it down. There is no consensus among style guides on how to spell it. The word has long dropped any pretence of being an abbreviation for anything, which is why it looks clunky to spell it with capitals and periods (O.K.) or even without periods (OK). In fiction, I write it phonetically as okay (a spelling Metcalf says is very recent, and which, incidentally, is the format preferred by The Globe and Mail Style Book).
This would seem verbose to frequent texters, though, who are habituated to writing simply k - or, in my favourite example of extreme compression in English, k? - to replace the full sentence "does this meet with your approval?"
An example of how texting combines truncation with phonetic spelling in a random way is the coda kthxbai - a formula that serves exactly the same function as the French " Veuillez agréer, monsieur, je vous prie, l'expression de mes sentiments les plus distingués."
I hear that online gamers are not happy with the accessibility of such codes and have taken to writing kk in their terse communications to mean OK, probably because it's confusing to outsiders - just as, hard as it is to imagine, OK itself must once have been.