O'clock is a squeezed-down form of of clock, which meant "by the clock". The of shrank to o' and stuck to the front of clock.
First, How Do You Say It?
uh-KLOK
It is said quickly, with the stress on clock. You will hear it in phrases such as at five o'clock and nine o'clock in the morning.
🌀 The Weird Part
Most contractions shorten the end of a word. Don't is do not with the o squeezed out, and it's is it is with the i squeezed out. In o'clock, the shrunken part is the first word instead: of became o'. That is unusual, and the apostrophe sits right at the join between the two pieces.
Some dictionaries say the phrase began as of the clock, and others say it began as plain of clock. Either way, o' is all that is left of of.
🕵️ Where Did It Come From?
- Early 1400s: of clok appears in writing. One early example is a 1419 proclamation by Henry V that says "at eyghte of clok".
- Early 1600s: the modern spelling o'clock settles down. A 1608 play has the line "'tis nine o'clock".
- Today: we say o'clock automatically, and most people never think about the words hiding inside it.
🗣️ Natural Examples
The meeting starts at nine o'clock.
We are leaving for school at eight o'clock sharp.
The shop closes at six o'clock on weekdays.
⚠️ Common Mistakes
Spelling.
❌ It is five of clock.
✅ It is five o'clock.
Spacing and apostrophe.
❌ It is five o' clock.
✅ It is five o'clock.
Half hours.
❌ It is five-thirty o'clock.
✅ It is half past five.
O'clock is only for exact hours. For 5:30, say half past five.
Useful Phrases
- at + o'clock: The film starts at seven o'clock.
- one o'clock, two o'clock, and so on, up to twelve o'clock.
- half past or quarter past for the times in between: a quarter past four.
If you are working out the phrase since nine o'clock compared with for nine hours, try Since vs For.
💬 In a Conversation
Sara: When does the bus leave?
Ravi: At three o'clock. Not three-thirty, that one is at half past.
Sara: Got it. Three o'clock, sharp.
🥡 The OddLingo Takeaway
Next time you say o'clock, you are saying of clock squeezed into one word. The apostrophe is the only clue left.