An indefinite and very long period of time, often used in a hyperbolic sense. It felt like eons had passed since they last met.
A major division of geological time, subdivided into eras. The Phanerozoic eon is the current eon in the geologic time scale.
A period of one billion years, especially in astronomy and cosmology. In astronomical terms, one eon equals roughly the time it takes light to traverse a megaparsec.