a state of eternal existence believed in some religions to characterize the afterlife
"Many devotees pray that their souls will find peace and joy in eternity after death."
a seemingly endless time interval (waiting)
"After hours in line for tickets, she realized that waiting felt like eternity."
Existence without end, infinite time.
"The stars will shine on into eternity, marking existence without end."
In plain English: Eternity is an endless amount of time that never stops or ends.
"She promised to love him for eternity."
The word eternity entered English through the path of Middle English and Old French before reaching its current form in Latin aeternitas. It replaced an earlier native term that had already fallen out of use, bringing with it a sense of endless duration from classical antiquity.