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.

Definitions of eon
  1. noun
    the longest division of geological time
    synonyms: aeon
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    Phanerozoic aeon
    the period from about 5,400 million years ago until the present
    Precambrian period
    the eon following the Hadean time and preceding the Phanerozoic eon; from about 3,800 million years ago until 544 million years ago
    Proterozoic aeon
    from 2,500 to 544 million years ago; bacteria and fungi; primitive multicellular organisms
    Archaeozoic aeon
    the time from 3,800 million years to 2,500 million years ago; earth's crust formed; unicellular organisms are earliest forms of life
    Priscoan aeon
    the earliest eon in the history of the Earth from the first accretion of planetary material (around 4,600 million years ago) until the date of the oldest known rocks (about 3,800 million years ago); no evidence of life
    type of:
    geologic time, geological time
    the time of the physical formation and development of the earth (especially prior to human history)
  2. noun
    an immeasurably long period of time
    “oh, that happened eons ago”
    synonyms: aeon
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    type of:
    age, long time, years
    a prolonged period of time
  3. noun
    (Gnosticism) a divine power or nature emanating from the Supreme Being and playing various roles in the operation of the universe
    synonyms: aeon
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    type of:
    spiritual being, supernatural being
    an incorporeal being believed to have powers to affect the course of human events
DISCLAIMER: These example sentences appear in various news sources and books to reflect the usage of the word ‘eon'. Views expressed in the examples do not represent the opinion of or its editors. Send us feedback
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