high noon

plural high noons

1. idiomaticExactly noon; midday (when the sun is at its highest).

   The same streets that are inviting and quiet at high noon may be intimidating at night.

   Synonyms: noontime, noontide, nones, 12 o'clock, 12 noon, 12 p.m., meridian, meridiem

2. figurativelyidiomaticThe zenith or apex of one's life or of a certain activity or era.

   Synonyms: noontime, noontide

3. idiomaticA time, set out in advance, at which an important decision is to be made or a nemesis is to be confronted.

   […] whereas, ten years since, there were thousands who could not endure my lightest word of rebuke to the South, they can now easily swallow John Brown whole, and his rifle into the bargain. In firing his gun, he has merely told us what time of day it is. It is high noon, thank God!

   1860 February 17 [1860 January 27], William Lloyd Garrison, “Speech of Wm. Lloyd Garrison, at the Annual Meeting of the Massachusetts Anti-Slavery Society, In the Tremont Temple, Boston, Jan. 27, 1860”, in The Liberator, volume XXX, number 7, page 26