OK

In the late 1830s, American newspapers ran a fashion for misspelled abbreviations. 'KG' for 'no go' (know go). 'OW' for 'all right' (oll wright). 'NS' for 'enough said' (nuff said). It was the era's bad pun. The Boston Morning Post on March 23, 1839, used 'o.k.' as shorthand for 'oll korrect'. The joke should have died with the rest of them.

Then Martin Van Buren ran for re-election in 1840. He grew up in a New York town called Kinderhook and his Democratic supporters formed clubs they named O.K. Clubs (Old Kinderhook). Banners and posters everywhere read O.K. The campaign joke amplified the newspaper joke. Van Buren lost the election. The abbreviation survived him.

The decisive accident was the telegraph. Operators needed short, unambiguous codes to confirm receipt of a message. O.K. happened to have no homophone, no rhyme, no easily-misheard variant. It was two consonants that sounded like nothing else. The 1840s commercial telegraph network drilled it into business English.

From there it spread by the usual American export channels: merchants, movies, occupation forces. By the 1950s it was on signs in Tokyo. By the 1990s it was the standard yes in Lagos and Helsinki. Linguists who study word borrowing say OK is unusual because almost every language took it as itself, not translated.

There is no equivalent journey for any other word. 'Hello' is younger but only widely used in English-speaking countries. 'Coca-Cola' is a brand. OK is a real word in two hundred languages, with no language asking it to behave.