Synonyms for Phantom:

adj.

ghostly (adjective)
ghostly.

n.

hallucination, a figment of your imagination, optical illusion, fantasy, fraud, falsehood, imaginings. mock, bogey, supernatural, hypothetical, Eidolon, Bogle, false, synthetic, fake, imaginary, revenant, visitant, beings, haunt, simulated, pretended, bogeyman. apparition (noun)
delusion.
cognition (noun)
shadow, apparition, Phantasm.
ghost (noun)
monster, chimera, horror, dracula, frankenstein, ghoul, vampire, illusion, apparition, succubus, terror, bugaboo, werewolf, ghost, hobgoblin, specter, bugbear, ogre, spirit, myth, daemon, nightmare, Phantasm, shadow, incubus, bogey man.
ghost; figment of the imagination (noun)
nightmare, haunt, specter, spirit, Eidolon, illusion, delusion, Phantasm, chimera, mirage, apparition, shadow, revenant, hallucination.
phantom (noun)
specter, spectre, unreal, apparition, shadow.
unsubstantiality (noun)
nullity, Nihility, impalpability, immateriality, nonexistence, mirage, intangibility, emptiness, cipher, nothingness, vacuity, zero, tenuousness, insignificance, Ethereality, unreality, spectre, vacancy.

Other synonyms:

Bogle, Eidolon, revenant, bogey, bogeyman. haunt, visitant. Other relevant words:
ghostly, apparition, imaginary, false, Bogle, visitant, delusion, supernatural, bogeyman, fantasy, Eidolon, unreal, revenant, doppelganger, haunt, hallucination, bogey.

Usage examples for phantom

  1. You will ask, how could a silent immaterial phantom effect that? – Green Tea; Mr. Justice Harbottle by Joseph Sheridan LeFanu
  2. For thousands of years men have enjoyed the light of the sun without letting the phantom of honor darken it. – Honor: A Play in Four Acts by Hermann Sudermann
  3. Already Earth doth seem A phantom place to me, And thy far home of dream, Is my reality. – The Ballad of the Quest by Virna Sheard