Noun

1. Existence without end, infinite time.
2. A period of time which extends infinitely far into the future.
3. (metaphysical) The remainder of time that elapses after death.
4. A comparatively long time.

   It's been an eternity since we last saw each other.

Usage notes

• In the sense "a comparatively long time", eternity is always used with the indefinite article (an eternity).

Synonyms

• (infinite time): all time
• (time extending infinitely far into the future): evermore, forever
• (remainder of time that elapses after death): afterlife
• (comparatively long time): an age, ages, centuries, donkey's years, hours, a lifetime, years, yonks