Aeon

The word aeon /ˈiːɒn/, also spelled eon (in American English) and æon, originally meant "life", "vital force" or "being", "generation" or "a period of time", though it tended to be translated as "age" in the sense of "ages", "forever", "timeless" or "for eternity". It is a Latin transliteration from the koine Greek word ὁ (ho aion), from the archaic αἰϝών (aiwon). In Homer it typically refers to life or lifespan. Its latest meaning is more or less similar to the Sanskrit word kalpa and Hebrew word . A cognate Latin word aevum or aeuum (cf. αἰϝών) for "age" is present in words such as longevity and mediaeval.

Although the term aeon may be used in reference to a period of a billion years (especially in geology, cosmology or astronomy), its more common usage is for any long, indefinite, period. Aeon can also refer to the four aeons on the Geologic Time Scale that make up the Earth's history, the Hadean, Archean, Proterozoic, and the current aeon Phanerozoic.

In astronomy an aeon is defined as a billion years (10⁹ years, abbreviated AE).

Roger Penrose uses the word aeon to describe the period between successive and cyclic big bangs within the context of conformal cyclic cosmology.

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