- an indefinitely long period of time; age.
- the largest division of geologic time, comprising two or more eras.
- Astronomy. one billion years.
- the usual US spelling of aeon
- geology the longest division of geological time, comprising two or more eras
1640s, from Latin aeon, from Greek aion “age, vital force, a period of existence, lifetime, generation;” in plural, “eternity,” from PIE root *aiw- “vital force, life, long life, eternity” (cf. Sanskrit ayu “life,” Avestan ayu “age,” Latin aevum “space of time, eternity,” Gothic aiws “age, eternity,” Old Norse ævi “lifetime,” German ewig “everlasting,” Old English a “ever, always”).
- The longest division of geologic time, containing two or more eras.