What does the O in "__ o'clock" stand for?

On the clock, like "on the line" for online.

Oh, look at the time.

"of the"

of the?

"Of" or "Of the"...it's like in names (O'Conner, O'Malley, O' Brian, O'Hara, etc.), In olden times people were often known by their first name and where they came from or lived like saying David of Malley...that eventually got changed to a last name and that is how we know it today.

On the clock.

My grandmother would say ten of five instead of ten to five. O means of or of the.

It is a short version for Of the clock.For example 6 o'clock is really 6 of the clock.

usally for OH No i am late again 😉

Of the. O is a common way of shortening of the.

Time is Irish.