t crops up in our speech dozens of times every day, although it apparently means little. So how did the word "OK" conquer the world, asks Allan Metcalf.

"OK" is one of the most frequently used and recognised words in the world.

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.

Visually, OK pairs the completely round O with the completely straight lines of K....