The ISBN of And Eternity is 978-0688086886.
The ISBN of Fragile Eternity is 9780061214653.
The ISBN of The Eternity Artifact is 978-0765353450.
The ISBN of Eternity - novel - is 0-445-20547-4.
You would say, "An eternity."
a eternity is a lifetime
Eternity is a noun.
infinity
Eternity - comics - was created in 1965.
The ISBN of The Summoned is 0-7434-0700-8.
The ISBN of Concrete Mathematics is 0201558025.
The ISBN of Glorifying Terrorism is 0955468809.
The ISBN of The Excalibur Alternative is 0671318608.