three o'clock

three o'clock (uncountable)

1. (In both the 12-hour clock and the 24-hour clock) The start of the fourth hour of the day; 3:00 a.m. (03:00).

   The front desk closes at three o'clock (= "The front desk closes at 3:00 a.m.").

2. (Only in the 12-hour clock) The start of the sixteenth hour of the day; 3:00 p.m. (15:00).

   The next train comes at three o'clock (= "The next train comes at 15:00").

3. (informal) To the right (horizontal clock orientation) (from the location of the 3 mark on a clock face)

   We've got a bogey at three o'clock.