You would say, "An eternity."
In the King James versionthe word - eternity - appears onceIsa 57:15 For thus saith the high and lofty One that inhabiteth eternity, whose name is Holy; I dwell in the high and holy place, with him also that is of a contrite and humble spirit, to revive the spirit of the humble, and to revive the heart of the contrite ones.
strength - 力量 [lì liàng] eternity - 永恒 [yǒng héng]
Eternity appears only once in Isaiah 57:15 in the King James version."For thus saith the high and lofty One that inhabiteth eternity, whose name is Holy; I dwell in the high and holy place, with him also that is of a contrite and humble spirit, to revive the spirit of the humble, and to revive the heart of the contrite ones."The word eternal appears 47 times.
"For what seemed like an eternity"
infinity
infinity
According to the World of Warcraft timeline (see related links) the game takes place roughly 10.000 years after the Well of Eternity was destroyed.
From Eternity to Here has 438 pages.
Eternity - novel - has 367 pages.
Passport to Eternity has 160 pages.
The Eternity Artifact has 367 pages.
The End of Eternity has 191 pages.
"And Eternity" by Piers Anthony has 320 pages.
Eternity Road - novel - has 416 pages.
From Here to Eternity - novel - has 861 pages.
millennium = 1,000 years eternity - forever your mom