eon

1. (US, informal, hyperbolic) A long period of time.Examples: "It’s been eons since we last saw each other."; "Traditionally, a luncheon is a lunch that takes an eon."USexcessiveinformal

2. (astronomy, geology) A period of one billion (short scale, i.e. 1,000,000,000) years.Examples: "We live our lives in three dimensions for our threescore and ten allotted years. Yet every branch of contemporary science, from statistics to cosmology, alludes to processes that operate on scales outside of human experience: the millisecond and the nanometer, the eon and the light-year."

3. (geology) The longest geochronologic unit, being a period of hundreds of millions of years; subdivided into eras.

4. (Gnosticism, usually spelled aeon or æon) A spirit being emanating from the Godhead.