/ ɪˈtɜːnəti; NAmE ɪˈtɜːrn-/ noun
1.
[ U ] ( formal ) time without end, especially life continuing without end after death :
There will be rich and poor for all eternity.
They believed that their souls would be condemned to burn in hell for eternity.
2.
an eternity [ sing. ] ( informal ) a period of time that seems to be very long or to never end :
After what seemed like an eternity the nurse returned with the results of the test.
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WORD ORIGIN
late Middle English : from Old French eternite , from Latin aeternitas , from aeternus without beginning or end, from aevum age.