A ghost or apparition.
"The phantom vanished into the fog, leaving no trace behind."
something apparently sensed but having no physical reality
"seemed to hear faint phantom bells"
"the amputee's illusion of a phantom limb"
Illusive.
"The phantom scent of fresh rain drifted through the dry, dusty room."
Nickname of the F-4B jet fighter flown by U.S. marines in Vietnam.
"The Phantom was the nickname given to the F-4B jet fighters that flew numerous missions over Vietnam."
Inherited from Middle English fantome, fanteme, from Old French fantosme, fantasme, from Latin phantasma ("an apparition, specter; (in Late Latin also) appearance, image"), from Ancient Greek φάντασμα (phántasma, "phantasm, an appearance, image, apparition, specter"), from φαντάζω (phantázō, "I make visible"). Doublet of phantasm.