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English definition of “o'clock”

o'clock

adverb     /əˈklɒk/ US  /-ˈklɑːk/
A1 used after a number from one to twelve to say the time when it is exactly that hour: It's two o'clock. He called me at four o'clock in the morning.Days and times of day
(Definition of o'clock adverb from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)
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