"Eternal Punishment"—the punishment of the age to come
Ilaria Ramelli, David Konstan, Terms for Eternity: aiônios and aïdios in Classical and Christian Texts. Piscataway, NJ: Gorgias Press, 2007.
Ilaria Ramelli is Assistant Professor of Ancient Philosophy at the Catholic University of Milan. David Konstan is the John Rowe Workman Distinguished Professor of Classics and the Humanistic Tradition, and Professor of Comparative Literature, at Brown University in Providence, Rhode Island.
The book examines the use of two Greek terms in classical Greek literature, LXX, NT, and early Christian literature.
I have not yet read it but I have read a few online overviews and reviews. I was encouraged to see that they argue that:
"Apart from the Platonic philosophical vocabulary, which is specific to few authors, aiónios does not mean 'eternal'; it acquires this meaning only when it refers to God, and only because the notion of eternity was included in the conception of God: for the rest, it has a wide range of meanings and its possible renderings are multiple, but it does not mean 'eternal.' In particular when it is associated with life or punishment, in the Bible and in Christian authors who keep themselves close to the biblical usage, it denotes their belonging to the world to come” (p. 238).
That is exactly in line with what I argued (very briefly) in The Evangelical Universalist. There I proposed that "eternal" life and "eternal" punishment made no reference to the duration of the life or punishment but only that the life and punishment are the life and punishment that belong to (i.e., occur during and are appropriate to) the age to come. So I am encouraged to find such a thorough academic study coming to the same conclusion.