Long time
'long time' is the definition.
(I know that eon is a type of long time)
This is the entire clue.
(Other definitions for eon that I've seen before include "Very long age" , "In time, long division" , "Era" , "Prolonged period" , "Geological period" .)
'long time' is the definition.
(a long period of time)
This is all the clue.
(Other definitions for era that I've seen before include "Period, age" , "Memorable period" , "Cycle" , "A particular period of time" , "Stage" .)
'long time' is the definition.
(an age is a period of time)
This is all the clue.
(Other definitions for age that I've seen before include "Years since birth" , "Historical period" , "Long period" , "16/18 [INDUSTRIAL REVOLUTION]" , "Length of life" .)