aeon

An aeon, also spelled eon, is a term for an indefinitely long period of time. In common usage it denotes a vast span that is difficult to measure. In technical contexts the word denotes specific scales of time. In geology, an eon is the longest division of the geologic time scale, typically spanning hundreds of millions to billions of years, and is subdivided into eras, periods, epochs and ages. The four recognized eons are the Hadean, Archean, Proterozoic, and Phanerozoic; the Phanerozoic is the current eon, extending from about 541 million years ago to the present. The term is rooted in the Greek aion, from which it is derived; the spelling aeon is often preferred in British English, while eon is common in American English.

In philosophy and theology, an aeon or aeon is a conceptual emanation or age-form, especially in Gnosticism and Neoplatonism, where it may refer to a divine order or a prolonged cosmic period. The use of the term in these contexts differs from the geological sense, but both retain the core sense of a vast, ordered span of time.

In modern usage, aeon/eon appears in literature, science fiction, and popular culture as a measure of enormous temporal scales or as a personified time-entity. The term remains a flexible linguistic tool for denoting time beyond ordinary human experience.