adverb NATO, ICAO, ITU & IMO radiotelephony code word used with numerals up to twelve to indicate direction
adverb 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!
adverb 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.
adverb 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.