TKG English Learner's Dictionary

o'clock

o'clockadverb

American /əˈklɑk/ British /əˈklɒk/
not gradable
common

  1. used after a number from one to twelve to give the time when it is exactly that hour

    O'clock is used only for whole hours: six o'clock, not six thirty o'clock, and only with the 12-hour clock: three o'clock in the afternoon, not fifteen o'clock. It can be left out when the meaning is clear: at six, at nine in the morning. It is not used together with a.m. or p.m.: six a.m., or six o'clock in the morning.

    not gradable [not gradable]

    Collocations

    phrase at six o'clock, by ten o'clock, around three o'clock, two o'clock sharp, one o'clock in the morning, the ten o'clock news

    Compare time

Word family

  • clock

Common mistakes

three thirty o'clock three thirty
O'clock is used only for the exact hour, never with minutes.
eight o'clock p.m. eight p.m.
O'clock is not used with a.m. or p.m.; say eight p.m. or eight o'clock in the evening.
fifteen o'clock three o'clock in the afternoon
O'clock goes only with the numbers one to twelve.

Word origin

Short for of the clock, that is, by the clock; the apostrophe marks the missing letters and explains the unusual spelling.

Checked against: Wiktionary, Online Etymology Dictionary (2026-09-16)

For translators

Grammar trap O'clock follows the number and is used only for exact hours from one to twelve, never with minutes or with the 24-hour clock. Many languages need a word for hour in every time expression; English uses o'clock only at the full hour and often drops it: at six.
Cultural background In speech, times are usually given on the 12-hour clock, with in the morning, in the afternoon, or at night added when it matters. The 24-hour clock appears mainly in timetables and never with o'clock.
Pronunciation trap Two syllables, uh-KLOCK, with the stress on the second; the o is the weak uh sound. The apostrophe is silent but must be written: o'clock, not oclock.