(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 four-o'clock

plural of twelve 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).

(In both the 12-hour clock and the 24-hour clock) The start of the tenth hour of the day; 9:00 a.m. (09:00).

(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 sixth hour of the day; 5:00 a.m. (05:00). / (Only in the 12-hour clock) The start of the eighteenth hour of the day; 5:00 p.m. (17:00).

(In both the 12-hour clock and the 24-hour clock) The start of the eleventh hour of the day; 10:00 a.m. (10:00).

(In both the 12-hour clock and the 24-hour clock) The start of the ninth hour of the day; 8:00 a.m. (08:00).

(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).