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.

How words evolve

Slang and contractions can form naturally without people being aware of it. This occurs as they quickly move through the less important parts of certain expressions. As Michael Adams, PhD, a professor of English and linguistics at Indiana University, pointed out, “It’s unusual for English speakers to retain a lot of words in unstressed positions in a phrase. In ‘1 of the clock,’ you’ve got two unstressed words there: the of and the the. And it is an invitation to a type of abbreviation. So it’s not ‘1 of the clock’ but ‘1 o’clock.’ You get that nice alternating rhythm there, which is so typical of the cadence of English.”

Have that in writing

As literacy rates increased over time, the spelling of “o’clock” became standardized. This shift resulted in the full phrase “of the clock” being used less frequently. “Part of what you have here is that, because these are early enough, the spelling comes to reflect the pronunciation,” explained Curzan.

Jack-o’-lantern

The term “O’clock” isn’t the only contraction that has largely replaced the original expression. “Jack-o’-lantern” also brings up the question: What does the “O” stand for? It actually represents “of,” making the full phrase “Jack of the lantern.”

This term originated in Britain during the 1800s to describe a night watchman or any man carrying a lantern, according to Merriam-Webster. Back then, it was common to refer to unfamiliar individuals as “Jack” or other popular names, much like the use of “John Doe” today. It wasn’t until the 19th century that “Jack-o’-lanterns” became the name for the now-iconic pumpkin lanterns. However, the exact link between the term and the pumpkins remains unclear.

More contractions

Contractions reveal how language evolves over time. Nowadays, we often overlook the apostrophe’s role in replacing something. However, expressions like o’clock, ne’er-do-well (“never-do-well”), and will-o’-the-wisp (“will-of-the-wisp”) highlight the rich history embedded in the English language. There’s much to admire about it, even though its grammar can drive us to frustration. (Why are there so many exceptions to “i after e except after c”?)