o'clock

Meanings

1. 1
   adv

   according to the clock, usually used at whole hour intervals

   It's three o'clock in Tokyo now.

2. 2
   adv

   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, i.e., at the hour.

   We are expected to be there at six o'clock in the morning!

3. 3
   adv

   Used to indicate that it is time to do a specific action, or time for a specific action to occur.

   I'm feeling peckish; I think it must be nearly dinner o'clock.

4. 4
   adv

   In conjunction with a numeral, indicates the direction, relative to the speaker or a vehicle, especially an aircraft, corresponding to the direction the hour hand is pointing at the time corresponding to the numeral, with twelve representing directly ahead on a horizontal plane, or directly up on a vertical plane, and three being to the right on either.

   It's at nine o'clock about two feet in from the edge of the branch. You need to know your "o'clocks" (nondigital) to spot birds.

Etymology

Shortened form of "of the clock", from Middle English of the clokke [from late 14th c.].