# eon

/ˈiɑn/ (US) · /ˈiːɒn/ (UK) · CEFR C1 · Noun

Source: https://englishreference.com/word/eon
Updated: 2026-05-30

## Definition

a very, very long period of time. It is often used to describe the age of the universe or the history of the Earth.

For teachers: an extremely long period of time, typically used in geological or astronomical contexts to describe vast chronological spans.

## Examples

- It felt like an eon since I last saw my friends.
- The geologist explained that the formation of the mountain range took place over several eons of tectonic pressure.
- While human history is measured in millennia, the universe itself has existed for billions of years, spanning an eon of cosmic expansion and stellar evolution.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.