Definition of eon in English:

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Pronunciation: /ˈēən/
(chiefly British also aeon)


(often eons)
1An indefinite and very long period of time, often a period exaggerated for humorous or rhetorical effect: he reached the crag eons before I arrived his eyes searched her face for what seemed like eons
More example sentences
  • It is deep time that makes possible the blind movement of evolution, the massing and honing of minute effects over eons.
  • And unlike a lot of rock on Earth that has been unrecognizably recycled by volcanic activity over the eons, a lot of lunar material retains records of some of the first impacts.
  • Consequently, in his view, for eons philosophers have in essence been barking up the wrong tree.
1.1 Astronomy & Geology A unit of time equal to a billion years.
Example sentences
  • This mass of molten continent still, however, retains enough homogeneity to be returned more or less as a unit at the mid-ocean ridges eons later as the rock cycle continues.
  • It's possible: Astronomers believe that comets and asteroids hitting the Moon eons ago left some water behind.
1.2 Geology A major division of geological time, subdivided into eras: the Precambrian eon
More example sentences
  • Despite our lack of knowledge, or perhaps because of it, researchers have divided the Precambrian into three time periods called eons.
  • The record has been much deformed, reconstituted, and obliterated during the subsequent Proterozoic and Phanerozoic eons.
  • Originally there were only two eons, the Precambrian and the Phanerozoic.
1.3 Philosophy (In Neoplatonism, Platonism, and Gnosticism) a power existing from eternity; an emanation or phase of the supreme deity.


Mid 17th century: via ecclesiastical Latin from Greek aiōn 'age'.

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