a clock

Adverb

o'clock (not comparable)

1. (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, i.e., at the hour.
   • We are expected to be there at six o'clock in the morning!
2. (humorous, informal) 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.
3. (with-numeral, one to twelve) 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.1989, Aileen R. Lotz, Birding around the year: when to find birds in North America