O Clock

For years we have all used the expression "O clock" when it comes to telling the time, but what does the O mean ? What does the O stand for in O clock ?

Its actually a shortening of "of the clock" as in 8 of the clock, it probably originated in the North Yorkshire region of the UK,, and used in the same way that they use t' to sub substitute "to the"..eg "I'm just going t' shop"