an apparition or specter.

a creation of the imagination or fancy; fantasy.

a mental image or representation of a real object.

an illusory likeness of something.

noun

apparition , bogey , bogeyman , bogle , eidolon , phantasma , phantom , revenant , shade , shadow , specter , spirit , visitant , wraith , daydream , fancy , fantasy , fiction , figment , illusion , reverie , vision , delusion , hallucination , ignis fatuus , mirage , will-o\'-the-wisp , dream , image , nightmare , vapor