Eidola is a noun that refers to an image, a figment of one's imagination, or a phantom. The word has no antonyms, as such, as it is a specific term used to describe a particular concept. However, one could use different words to describe the opposite of the concept. For example, one could use words like "reality," "truth," or "authenticity" to describe the antithesis of eidola. These words imply the idea of substance, veracity, and certainty, whereas eidola is more concerned with illusion and imagination. Therefore, while there are no direct antonyms for the term, its opposite could be adequately captured by various other words.