o'clock

Từ điển Oxford Advanced Learner 8th

o'clock [o'clock] BrE [əˈklɒk] NAmE [əˈklɑːk] adverb
used with the numbers 1 to 12 when telling the time, to mean an exact hour
• He left between five and six o'clock.
•at/after/before eleven o'clock