noun.
A point of time from which succeeding years are numbered; especially, a point of time distinguished by some remarkable event, or the event itself as distinguishing the time of its occurrence.
noun.
Hence A specific period of time; any space of time considered as a unit with reference to some particular characteristic or course of events.
noun.
In geology, specifically, one of the shorter divisions of geological time.
noun.
In astronomy, an arbitrary fixed date, for which the elements of a planetary or cometary orbit, or of any motion, are given.
noun.
See the adjectives.
noun.
See equivalent phrases under era.
noun.
Synonyms Epoch, Era, Period, Age. Epoch and era should be distinguished, though in common usage they are interchanged. “An era is a succession of time: an epoch is a point of time. An era commonly begins at an epoch. We live in the Christian era, in the Protestant era, in the era of liberty and letters. The date of the birth of Christ was an epoch: the period of the dawn of the Reformation was an epoch” (A. Phelps, Eng. Style, p. 365). Period may be the opposite of epoch, in being the date at which anything ends, or it may be mere duration, or duration from point to point; the word is very free and often indefinite in its range of meaning. The meaning of age is modified by its connection with human life, so as often to be associated with a person: as, the age of Pericles; but it is also freely applied to time, viewed as a period of some length: as, the bronze age; the golden age; this is an age of investigation.
noun.
In the mechanics of vibration, a term introduced into the equation for a simple harmonic motion in cases where time is not reckoned from the instant when the vibrating particle has reached its greatest positive elongation.