twelve o'clock

twelve o'clock (usually uncountable, plural twelve o'clocks)

1. (In both the 12-hour clock and the 24-hour clock) The start of the thirteenth hour of the day; noon (noontime); 12:00 p.m. (12:00).

   The next train comes at twelve o'clock (= "The next train comes at noon").

2. (Only in the 12-hour clock) The start of the first hour of the day; midnight; 12:00 a.m. (00:00).

   The bar closes at twelve o'clock (= "The bar closes at midnight").

3. (informal) A position straight ahead (horizontal clock orientation) or above (vertical clock orientation) (from the location of the 12 mark on a clock face)

   We've got a bogey at twelve o'clock (= "We've got a bogey straight in front of us").

The concepts of twelve o'clock high and high noon have similar-sounding names but differ in meaning and in derivation. The first means "straight ahead and above" and the second means "exactly noon, when the sun is higher in the sky than at any other moment of the day".