phan·tasm 
(făntăz′əm)
(făntăz′əm)n.
1. Something apparently seen but having no physical reality; a phantom or an apparition. Also called phantasma.
2. An illusory mental image. Also called phantasma.
3. In Platonic philosophy, objective reality as perceived and distorted by the five senses.
[Middle English fantasme, from Old French, from Latin phantasma, from Greek, from phantazein, to make visible, from phantos, visible, from phainein, to show; see bhā-1 in the Appendix of Indo-European roots.]
phan·tasmal (făn-tăzməl), phan·tasmic (-tăzmĭk) adj.