The word aeon /ˈiːɒn/, also spelled eon (in American and Australian English), 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 ancient Greek word ὁ αἰών (ho aion), from the archaic αἰϝών (aiwōn) meaning "century". In Greek, it literally refers to the timespan of one hundred years. A cognate Latin word aevum (cf. αἰϝών) for "age" is present in words such as eternal, longevity and mediaeval.
Although the term aeon may be used in reference to a period of a billion years (especially in geology, cosmology and 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.
