Eidolon

In ancient Greek literature, an eidolon (/aɪˈdoʊlɒn/;[1] Ancient Greek: εἴδωλον 'image, idol, double, apparition, phantom, ghost'; plural: eidola or eidolons) is a spirit-image of a living or dead person; a shade or phantom look-alike of the human form.

[2][3] Both Euripides and Stesichorus, in their works concerning the Trojan Horse, use the concept of the eidolon to claim that Helen was never physically present in the city at all.

[2] Homer's use of eidola also extends to the Odyssey where, after the death of the suitors of Penelope, Theoclymenus notes that he sees the doorway of the court filled with them.

[5] In Dream-Land, an 1844 poem by Edgar Allan Poe, an Eidolon rules over a realm haunted by "ill angels only" and reserved for the ones whose "woes are legion" and who "walk in shadow".

In Whitman's use of the term we can see the use broaden to include the concept of an oversoul composed of the individual souls of all life and expanding to include the Earth itself and the hierarchy of the planets, Sun, stars and galaxy.