The English language has many tricky aspects, such as words that look like they rhyme but don’t, and words spelled the same but pronounced differently. It also has confusing idioms. Even native speakers may wonder about phrases like “o’clock,” which uses an apostrophe to indicate that something has been omitted—something many people no longer remember.

The apostrophe has two main uses: to show possession (e.g., “children’s books”) and to indicate missing letters in contractions (e.g., “don’t” for “do not”).

What is o’clock short for?

The letter “O” in “o’clock” stands for “of the,” as explained in the Britannica Dictionary. So, when someone says it’s six o’clock, they are essentially saying it’s “six of the clock.” While this may sound strange to contemporary English speakers, “of the clock” was simply another way of saying “according to the clock.”

The origin of “of the clock”

The term “predictably” first emerged as mechanical clocks gained popularity in Europe during the late 1300s. Prior to that era, time was typically measured using sundials or shadow clocks. As time progressed, analog clocks became the dominant method for tracking time, which led to the widespread use of the phrase “of the clock.”

The origin of “o’clock”

As with many types of slang, the awkward-sounding “of the clock” quickly became shortened to “o’clock.” This phrase is commonly used when stating the time or scheduling appointments—both in the past and today. The abbreviation emerged to make conversations faster and more fluid.

“Because it’s a set phrase for telling time, it’s not surprising that it got shortened over time because we’re saying it fast,” explains Anne Curzan, PhD, a professor of English, linguistics, and education at the University of Michigan, in an interview with Reader’s Digest.