eidolon

noun

1. An image or representation of an idea; a representation of an ideal form; an apparition of some actual or imaginary entity, or of some aspect of reality.

   “As a species it is extinct; as an eidolon it retains its corporeality – but only if maintained in a state of equipoise.”

   “It was not hard to forge her image, her "eidolon", in the grey gloom of the little church.”

   “[…]Kit was sitting up staring into the dark at this eidolon, inelegantly turned out contrary to a whole raft of public-decency statutes, which had come monitory and breathing in to violate Kit's insomnia.”

2. A phantom; a ghost or an elusive entity.

   “Was Philippe d'Orleans seen, this day, 'in the Bois de Boulogne, in grey surtout;' waiting under the wet sere foliage, what the day might bring forth? Alas, yes, the Eidolon of him was,—in Weber's and other such brains.”

3. An unsubstantial image; a spectre; a phantom.