(modifying a numeral, one to twelve) In conjunction with a numeral, indicates the time within a twelve-hour period (midnight to noon or noon to midnight), specifically the time when the hour hand of a clock points precisely to the symbol or marking corresponding to the designated numeral.

plural of twelve o'clock

The time to begin social drinking.

(archaic) what's the time?

Alternative form of four o'clock

(slang, humorous) The time of the first beer (or alcoholic beverage) of the day. / (slang, humorous) Time for a beer (the first of the day or otherwise).

(informal, humorous) A time of day, usually during the night or early in the morning, considered unreasonable or when one is prone to poor judgment.

(slang, humorous) The time of the first glass of wine (or alcoholic beverage) of the day.

(In both the 12-hour clock and the 24-hour clock) The start of the third hour of the day; 2:00 a.m. (02:00). / (Only in the 12-hour clock) The start of the fifteenth hour of the day; 2:00 p.m. (14:00).

(In both the 12-hour clock and the 24-hour clock) The start of the twelfth hour of the day; 11:00 a.m. (11:00).