Nouns

(n)apparition, phantom, phantasm, phantasma, fantasm, specter, spectrea ghostly appearing figure“we were unprepared for the apparition that confronted us”
(n)apparition, phantom, phantasm, phantasma, fantasm, shadowsomething existing in perception only“a ghostly apparition at midnight”

Adjectives

(s)phantomsomething apparently sensed but having no physical reality“seemed to hear faint phantom bells”, “the amputee's illusion of a phantom limb”