Allan Metcalf has recently written a book about the history of the word "okay" (in its various spellings). He has summarized his findings in an article for the BBC. This word, Metcalf argues, is phonetically structured in such a way that gave it the ability to easily transcend linguistic boundaries:

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.

Metcalf's article briefly traces the development of the word, but also states his claim of its true origin:

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. (all correct)".

Link via First Things | Photo by Flickr user A National Acrobat used under Creative Commons license