Dictionary
e•on
Pronunciation: (ē'un, ē'on), [key]—
n.
1. an indefinitely long period of time; age.
2. the largest division of geologic time, comprising two or more eras.
3. Astron.one billion years.
Also,aeon.Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.