Is it ensure, insure, or assure?
early 14c., "illusory appearance," from Old French fantaisie (14c.) "vision, imagination," from Latin phantasia, from Greek phantasia "appearance, image, perception, imagination," from phantazesthai "picture to oneself," from phantos "visible," from phainesthai "appear," in late Greek "to imagine, have visions," related to phaos, phos "light," phainein "to show, to bring to light" (see phantasm). Sense of "whimsical notion, illusion" is pre-1400, followed by that of "imagination," which is first attested 1530s. Sense of "day-dream based on desires" is from 1926.
fantasy fan·ta·sy (fān'tə-sē, -zē)
Imagery that is more or less coherent, as in dreams and daydreams, yet unrestricted by reality. Also called phantasia.