The word eidolon relates with Hades himself (aidoneus) and with eidos, ideational forms and shapes, the ideas that form and shape life, but are so buried in it that we only ‘see’ them when pulled out in abstractions.
Hillman derives the psychological significance of Aidoneus from its root connection to eidolon and eidos, making the god’s name the etymological ground for a depth-psychological theory of image and invisible form.
, The Dream and the Underworld, 1979thesis