eon

American  

[ee-uhn, ee-on] / ˈi ən, ˈi ɒn /

Or aeon

noun

eons plural

1. an indefinitely long period of time; age.

2. the largest division of geologic time, comprising two or more eras.

3. Astronomy. one billion years.

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eon British  

/ ˈiːən, ˈiːɒn /

noun

1. the usual US spelling of aeon

2. geology the longest division of geological time, comprising two or more eras

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eon Scientific  

/ ē′ŏn′ /

1. The longest division of geologic time, containing two or more eras.

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Usage

What does eon mean? Eon is commonly used in a general way to refer to an indefinitely long period of time. Outside of science, people usually use eon as a way to exaggerate how long something took to happen or how long something lasted. In the context of geology, eon refers to the largest division of geological time. Technically speaking, an eon is made up of two or more eras, which consist of several periods, which are divided into epochs. All of these units of time vary as to their exact length, but most consist of at least millions of years, with eons lasting billions or hundreds of millions of years. In the context of astronomy, an eon is one billion years. Example: It took me eons to get a straight answer as to how long an eon actually is.

Other Word Forms

Noun Inflected Forms

• eons
  plural

Etymology

Origin of eon

see origin at aeon

Explanation

An eon is a really, really, super-long, impossible-to-measure length of time. If you sit down to dinner hanging your head and moaning that it's been an eon since you ate anything, you’re exaggerating. Four hours ago is not an eon. Eon goes back to the Greek aiōn, "age." An age is not easy to measure, and neither is an eon. Both are just really long periods of time, but in science an eon is about a billion years. You can use the noun eon for anything that takes a long while, including how long it will be before another planet collides with Earth or how many days until summer vacation starts — one is an eon, the other feels like an eon, or forever.

Example Sentences

See Examples For:

eon eons

But it would be three long years — a veritable eon during that pre-MTV era — before Harrison released the LP’s worthy successor.

From Salon ● Nov. 15, 2024

WIMBLEDON, England — The streak lived for 132 days or, in tennis time, an eon.

From Washington Post ● Jul. 2, 2022

When I started reporting on elections an eon ago, smartphones didn’t exist and a desktop was a typewriter.

From Los Angeles Times ● Jun. 20, 2022

In the eon between 1.8 and 0.8 billion years ago—a time dubbed the "boring billion"—the continents seemed to grow progressively thinner.

From National Geographic ● Feb. 11, 2021

An hour in Mrs. Ysidro’s AP Calculus was an eon.

From "A Heart in a Body in the World" by Deb Caletti

As Lippman puts it, "It's a new window into the evolution of life across eons and a new opportunity to more efficiently engineer or fine-tune crop traits."

From Science Daily ● Mar. 14, 2026

Tanking’s been around for eons, though league commissioner Adam Silver said recently it has gotten “worse.”

From The Wall Street Journal ● Mar. 2, 2026

Harold Prince’s 1979 Broadway premiere, starring Len Cariou and Angela Lansbury, seems like eons ago in terms of creative possibility.

From Los Angeles Times ● Feb. 3, 2026

For eons, most investors treated hot stocks the same way.

From Barron's ● Jan. 28, 2026

Shaped through long eons of evolution, our genes not only make us what we are, but hold in their minute beings the future — be it one of promise or threat.

From "Silent Spring" by Rachel Carson