Stretch of time
(Other definitions for eon that I've seen before include "An immense time" , "Vast age; eternity" , "In time, long division" , "Vast age (alt. sp.)" , "Huge time period" .)
(Other definitions for era that I've seen before include "Aeon" , "Are involved in time span" , "Geological period" , "8" , "Important historical period" .)