English is full of quirks that native speakers often take for granted.

Words that look like they should rhyme, like come and home or through and cough, don’t.

Others, like tear and tear or wound and wound, are spelled the same but pronounced differently depending on the context.

Add in peculiar idioms like “cold turkey” or “raining cats and dogs,” and it’s no wonder English can confound even its native speakers, let alone learners

The Role of the Apostrophe

Quick grammar refresher: Apostrophes serve two main purposes.

They indicate possession, as in “children’s toys” or “the director’s film,” and they replace omitted letters in contractions like “don’t” (do not) or “there’s” (there is).

The apostrophe in o’clock serves the latter purpose, signaling that part of the original phrase has been dropped—though many people have forgotten what that was.

What Does “O’Clock” Mean?

The “O” in o’clock stands for “of the,” according to the Britannica Dictionary. So when someone says “it’s six o’clock,” they’re actually saying “it’s six of the clock.” While this phrasing might sound unusual to modern ears, it was once a common way of saying “according to the clock.”

The Origin of “Of the Clock”

This phrase emerged when mechanical clocks became widespread in Europe during the late 1300s.

Before then, people relied on sundials and shadow clocks to track time.

But as analog clocks became the standard, the phrase “of the clock” gained traction to specify timekeeping based on these devices.

How “Of the Clock” Became “O’Clock”

As is typical with language, the lengthy phrase “of the clock” was eventually shortened to o’clock for simplicity. People used the phrase frequently when telling time or scheduling events, and the abbreviated version made conversations smoother.

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

The Evolution of Words

Slang and contractions often develop naturally as people skip over less significant parts of phrases in casual speech. Michael Adams, PhD, a professor of English and linguistics at Indiana University, elaborates: “It’s unusual for English speakers to retain many words in unstressed positions in a phrase. In ‘1 of the clock,’ you’ve got two unstressed words: of and the. That creates an invitation for abbreviation. So instead of saying ‘1 of the clock,’ it becomes ‘1 o’clock.’ This rhythmic alternation is typical of English.”

The Role of Writing in Standardization

As literacy spread, written language played a significant role in cementing o’clock as the standard. The more people wrote it, the less frequently the full phrase of the clock was used. “Because these phrases emerged early enough, the spelling adapted to match the pronunciation,” Curzan explains.

Jack-o’-Lantern and Other Contractions

O’clock isn’t the only contraction that has outlived its original phrase. Take Jack-o’-lantern, for instance. The “O” once again stands for “of,” making the full term “Jack of the lantern.”

The phrase originated in Britain in the 1800s, where it referred to a night watchman or any man carrying a lantern, according to Merriam-Webster. At the time, strangers were often dubbed “Jack” or other generic names, much like “John Doe” today. It wasn’t until the 19th century that the term Jack-o’-lantern came to describe the carved pumpkins we know today.

The Legacy of Contractions in English

Contractions like o’clock highlight how language evolves over time. Today, we’re so accustomed to apostrophes that we often forget they replace omitted words. Phrases like o’clock, ne’er-do-well (never-do-well), and will-o’-the-wisp (will-of-the-wisp) reveal the rich history behind the English language—quirks and all.

Despite its many exceptions and eccentricities, the evolution of English offers much to appreciate, even as its grammar sometimes leaves us scratching our heads. (Why are there so many exceptions to “I before E except after C”?)