The “o” in “o’clock” is a shortened way of saying “of the” , from the older phrase “of the clock.”

What does the “o” in “o’clock” mean?

Historically, people would say things like “It is 3 of the clock” to make clear they were giving the time according to a mechanical clock, not by a sundial, the sun’s position, or rough guessing. Over time, English speakers compressed that phrase in speech, and “of the clock” became “o’clock,” with the o’ standing in for “of the.”

So when you say “It’s 5 o’clock,” you’re really saying “It’s 5 of the clock” in an old-fashioned, contracted form.

How the phrase evolved

  • Early timekeeping often relied on sundials or just the position of the sun.
  • When mechanical clocks spread, it became useful to specify time “of the clock.”
  • In everyday speech, that longer phrase naturally shortened to “o’clock,” just as many common expressions contract over time.

A modern parallel is how “do not” becomes “don’t”; here, “of (the)” became o’.

Common misconceptions and fun side-notes

People online sometimes guess that the o stands for things like “zero” or a mysterious symbol, especially because of digital time formats like “0700 hours,” but that’s a separate convention and not related to “o’clock.” Others jokingly tie it to Irish-style surnames like “O’Connor,” but that’s just playful confusion, not etymology.

In short, “o’clock” = “of the clock,” a little surviving fossil from the early days of precise timekeeping.

Information gathered from public forums or data available on the internet and portrayed here.