early 13c., fantesme, from Old French fantosme "a dream, illusion, fantasy; apparition, ghost, phantom" (12c.), and directly from Latin phantasma "an apparition, specter," from Greek phantasma "image, phantom, apparition; mere image, unreality," from phantazein "to make visible, display," from stem of phainein "to bring to light, make appear; come to light, be seen, appear; explain, expound, inform against; appear to be so," from PIE root *bha- (1) "to shine" (cf. Sanskrit bhati "shines, glitters," Old Irish ban "white, light, ray of light"). Spelling conformed to Latin from 16c. (see ph). A spelling variant of phantom, "differentiated, but so that the differences are elusive" [Fowler].
phantasm phan·tasm (fān'tāz'əm)
Something apparently seen but having no physical reality; an apparition.
An illusory mental image.