Aeon

The word aeon ( /ˈiːɒn/), also spelt eon or æon, originally means "life", and/or "being", though it then tended to mean "age", "forever" or "for eternity". It is a Latin transliteration from the koine Greek word ὁ αἰών (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 olam. A cognate Latin word aevum or aeuum (cf. αἰϝών) for "age" is present in words such as longevity and mediæval.

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.