Wiktionary
n. The first hour of the day in both the 12-hour and the 24-hour clock and also noon in the 12-hour clock; 12:00.
Usage examples of "twelve o'clock".
We'll still have time to see if she's at home to take the twelve o'clock call.
On the gangway the master lowered his sextant, walked aft to Mr Hervey and said, 'Twelve o'clock, sir: fifty-eight minutes north.
The first lieutenant turned to Jack, took off his hat, and said, 'Twelve o'clock, sir, if you please, and fifty-eight minutes north.
When presently she came back to the reality of things she looked at her watch and saw that it was close on twelve o'clock.
The officers took their altitudes: Pullings reported that the sun was on the meridian: Jack allowed that it was twelve o'clock and that the new naval day might now begin.
It was twelve o'clock the next day when our train steamed into Pashet station.
Anyway, what's noon, sun-time - it's certainly not twelve o'clock on our watches?
About eleven or twelve o'clock the members of other Committees come in.