A phantom, ghost, or illusion; a shadowy image or specter, often used poetically to describe something unreal or insubstantial.
From Greek 'eidolon' meaning phantom or shade, derived from 'eidos' (form). The word entered English literature through translations of Greek texts and became popular in poetry and philosophy.
Edgar Allan Poe loved using 'eidolon' because it's one of the few English words that sounds like what it means—haunting, echoing, a little bit unreal—making it perfect for gothic literature.
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