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

Synonyms

• forever
• months
• long
• age

Examples of eon in a Sentence

Recent Examples on the Web

The Rays lost for the 12th time in their last 16 games and 26th in 37 since the end of their majors-best 25-9 run in late June, which seems eons ago. —Marc Topkin, The Orlando Sentinel, 10 Aug. 2025

Two new studies offer the most detailed glimpse yet of how Earth’s climate and sea levels have changed during the Phanerozoic — the latest geologic eon covering the time period from 538.8 million years ago to the present. —David Bressan, Forbes.com, 17 July 2025

That may not seem like that long for some franchises or fanbases, but it’s been eons in Bronx years. —Gary Phillips, New York Daily News, 27 Mar. 2025

The Southern Everglades and Florida Bay, which for eons had received that water, grew parched, leading to environmental and economic degradation there as well. —Bill Kearney, Sun Sentinel, 29 June 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