o'clock
UK: əˈklɒk | US: əˈklɑːk
adv. used to indicate the exact hour when telling time (short for "of the clock")
The term "o'clock" originated in the late 14th century as a contraction of the Middle English phrase "of the clock," distinguishing clock time from natural time (e.g., solar or ecclesiastical time). The apostrophe replaces "f" in "of," a common contraction in older English (e.g., "o'er" for "over"). "Clock" derives from Old French "cloque" (bell) or Medieval Latin "clocca," reflecting early clocks' reliance on bell strikes to mark hours. The phrase solidified as a standard time-telling convention by the 16th century.
The meeting starts at three o'clock sharp.
She wakes up every morning at six o'clock.
"What time is it?" "It's nearly twelve o'clock."
The train departs at nine o'clock tonight.
By five o'clock, the office was empty.