phantom
noun /ˈfæntəm/
  /ˈfæntəm/
- a ghost- the phantom of his dead father
 
- a thing that exists only in your imagination- Phantoms and chimeras inhabited her brain.
 
Word OriginMiddle English (also in the sense ‘illusion, delusion’): from Old French fantosme, based on Greek phantasma, from phantazein ‘make visible’, from phainein ‘to show’.