Very big stretch (3)
(Other definitions for eon that I've seen before include "Vast period" , "thousand million years" , "Major division of geological time" , "Vast age (alt. sp.)" , "Era" .)
(Other definitions for aeon that I've seen before include "Immeasurably long period of time" , "Vast time period" , "An age; period" , "Epoch" , "A very long time, an age" .)