eternity

Etymology

From Middle English eternyte, from Old French eternité, from Latin aeternitās. Displaced native Old English ēcnes.

noun

1. (uncountable) Existence without end, infinite time.
   Eternity has generally been considered as divisible into two parts; which have been termed, eternity a parte ante, and eternity a parte post: that is, in plain English, that eternity which is past, and that eternity which is to come. 1829, John Wesley, Sermons on Several Occasions, 10th edition, volume 2, Sermon LVIII: On the Eternity of God, page 1
   This theory regards creation as an act of God in eternity past. 1886, Augustus Hopkins Strong, Systematic Theology: a Compendium and Commonplace-book Designed for the Use of Theological Students, page 190
   Those who like not the company of the saints on earth will get none of it in eternity; but, as godless company is their delight now, they will afterwards get enough of it, when they have eternity to pass in the roaring and blaspheming society of devils and reprobates in hell. 2000, Thomas Boston, Human Nature in Its Fourfold State, page 247
2. (uncountable, philosophy, theology) Existence outside of time.
   We sometimes speak of eternity in contradistinction to time; and often say, "through time and into eternity;" and again "from eternity to eternity," which is simply another form of expressing the same idea, and "pass through time into eternity." in other words, time is a short period allotted to man in his probationary state—and we use the word time in contradistinction to the word eternity, merely for the accommodation of man in his finite sphere, that we may comprehend and learn to measure periods. 1879, Erastus Snow, “Rest Signifies Change, etc.”, in Brigham Young, editor, Journal of Discourses, volume 21, published 1881
3. (countable) A period of time which extends infinitely far into the future.
4. (metaphysical) The remainder of time that elapses after death.
5. (informal, hyperbolic) A comparatively long time.
   It's been an eternity since we last saw each other.