It is also one of the oddest expressions ever invented. But this oddity may in large measure account for its popularity.
It's odd-looking. It's a word that looks and sounds like an abbreviation, an acronym.
We generally spell it OK - the spelling okay is relatively recent, and still relatively rare - and we pronounce it not "ock" but by sounding the names of the letters O and K.
So both in speech and in writing OK stands out clearly, easily distinguished from other words, and yet it uses simple sounds that are familiar to a multitude of languages.
Almost every language has an O vowel, a K consonant, and an A vowel. So OK is a very distinctive combination of very familiar elements. And that's one reason it's so successful. OK stands apart.
Ordinarily a word so odd, so distinctive from others, wouldn't be allowed in a language to begin with. As a general rule, a language allows new words only when they resemble familiar ones.
On 23 March 1839, OK was introduced to the world on the second page of the Boston Morning Post, in the midst of a long paragraph, as "o.k. (meaning all correct)".
But in the 20th Century OK moved from margin to mainstream, gradually becoming a staple of nearly everyone's conversation, no longer looked on as illiterate or slang.
Its true origin was gradually forgotten. OK used such familiar sounds that speakers of other languages, hearing it, could rethink it as an expression or abbreviation in their own language.
OK allows us to view a situation in simplest terms, just OK or not.
When someone falls down, the question is not "how well are you feeling?" but the more basic "are you OK?". And any lingering stigma associated with OK is long since gone.
