From WordNet (r) 3.0 (2006):
phantom
adj 1: something apparently sensed but having no physical
reality; "seemed to hear faint phantom bells"; "the
amputee's illusion of a phantom limb"
n 1: a ghostly appearing figure; "we were unprepared for the
apparition that confronted us" [syn: apparition,
phantom, phantasm, phantasma, fantasm, specter,
spectre]
2: something existing in perception only; "a ghostly apparition
at midnight" [syn: apparition, phantom, phantasm,
phantasma, fantasm, shadow]