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OK is perhaps the best-known abbreviation in the English language.
But if you try to pin down a passerby as to what it actually means, many are hard-pressed for an answer.
Some think it comes from "all clear".
Others think it's a derivative of Scots from "och aye", or Greek "olla kalla", or that it's from the Choctaw word "okeh".
Someone found the answer for good in the 1960s, when Allen Walker Read, a Columbia University etymologist wrote it in the journal American Speech.
In 1838, newspaper editors in Boston, Massachussetts, thought abbreviations were very in.
An editor would regularly write G.T.D.H.D., or
Give the Devil his Due
or they may write S.P., meaning:
They took to spelling all correct as if it were spelled "oll korrect" or "orl korrect" as way of a in-joke, using OK as a shorthand.
In addition, the phrase was popularised by President Martin Van Buren's nickname "Old Kinderhook", which in 1840 took root as a timely campaign slogan - OK.
His supporters started the 'OK club' and the term has been about ever since.
Sounds a bit tenuous now, doesn't it?
Watch the full video, below:
More: What the 'E' in the top corner of your phone's screen really means