eon

noun

ˈē-ən  ˈē-ˌän 

variants or chiefly British aeon

1

: an immeasurably or indefinitely long period of time : age

I haven't seen him in eons.

2

a

: a very large division of geologic time usually longer than an era

the Archean eon

b

: a unit of geologic time equal to one billion years

Examples of eon in a Sentence

Recent Examples on the Web

But neither a chart of geology’s eons, eras, and periods, nor a calculus of infinitesimals, can eliminate a sense of awe in the face of geological time. —Lewis Hyde, Harpers Magazine, 18 June 2025

Thanks to Gaia, scientists now can better gauge the amount of dark matter within our galaxy and have been able to track the Milky Way’s growth and evolution across eons via relic streams of stars strewn from ancient mergers with other, smaller galaxies. —Lee Billings, Scientific American, 18 June 2025

It should be noted that time in Hell works differently, and when he's eventually brought into another Earth's dimension, eons could've passed for him. —Fran Ruiz, Space.com, 28 Mar. 2025

From these vantage points, old and new Aspen converge in a panoramic sweep of mountains that have towered here for eons, rooftops of condos that sprang up in recent years, a swirl of tourists mingling with longtime locals. —Spencer Elliott, Forbes, 9 Mar. 2025

Word History

Etymology

borrowed from Late Latin aeōn "age (in the world's history), evil spirit (in Gnosticism)," borrowed from Greek aiṓn "lifetime, long period of time, age" — more at aye entry 3

First Known Use

circa 1642, in the meaning defined at sense 1

Rhymes for eon

• adlerian
• caesarian
• cyclopean
• empyrean
• euclidean
• european
• grammarian
• hercynian
• huronian
• jacobean
• kampuchean
• maccabean

Kids Definition

eon

noun

ˈē-ən

1

: a very long period of time

2

a

: a very large division of geologic time usually longer than an era

b

: a unit of geologic time equal to one billion years