A time, set out in advance, at which an important decision is to be made or a nemesis is to be confronted
Exactly noon; midday (when the sun is at its highest).
The zenith or apex of one's life or of a certain activity or era.
The upper limit of a sequence of real numbers is the real number which can be found as follows: remove the first term of the sequence in order to obtain the "first subsequence." Then remove the first term of the first subsequence in order to obtain the "second subsequence." Repeat the removal of first terms in order to obtain a "third subsequence," "fourth subsequence," etc. Find the supremum of each of these subsequences, then find the infimum of all of these supremums. This infimum is the upper limit.