The word “Ok / Okay” has been named the most recognized word on the planet after beating second place: “Coca-cola”. In fact, Coca-Cola even released the OK Soda drink from 1993-1995 in an eventually unsuccessful attempt to own both terms. Despite its popularity, if you ask most people where Ok came from, or what it stands for, they’ll likely have no clue.
First, most languages have the sounds required to form the word, this has no doubt helped it maintain its presence along with its convenience. However, its origins are a little more interesting.
In 1839, the Boston Morning Post introduced Ok as “o.k. (all correct)”. This little irony-based joke (o.k. standing for the misspelled ole kurrek) would likely have disappeared alongside the majority of the Boston paper’s other bizarre abbreviations, if not for a certain presidential candidate.
In 1840, President Martin Van Buren tried for his second term of the presidency as he ran against William Henry Harrison. Van Buren was raised in Kinderhook, New York, and had so developed the nickname Old Kinderhook. This inspired “O.K. Clubs“ to pop up across the states and gave a new meaning to Ok.
However, Harrison’s team also decided to start using Ok, but they created their own myth that would spread far. In fact, the few who believe they know the origin of Ok today will likely cite some version of this tale (there are in fact several other myths about the word’s origin which are certainly interesting to research). Harrison’s team rumoured that President Andrew Jackson, the mentor of President Van Buren, was so poor at spelling that he signed “O.K.”, as an abbreviation of the aforementioned ole kurrek (which he supposedly believed to be the correct spelling), at the bottom of presidential papers to indicate his approval. In the end, Old Kinderhook was unsuccessful in his run and the presidency was handed to William Henry Harrison… but OK lived on.
So as we know, Ok was the original from which okay was derived and funnily enough stands for “all correct” (in a roundabout kind of way). I suppose you could say that's enough to argue that the shorter form is more correct. Supporting this, it is Ok and not Okay that is listed first in the Oxford dictionary. You’ll struggle to find many instances of the word in formal writing to give a definite answer, and I can’t find a reason for adding the final two words other than natural evolution, so irritatingly we might just have to admit that both are acceptable (but ok is clearly correct ;) ).
Sources: history.com, qz.com, bbc.co.uk