Fantastic
late Middle English (in the sense ‘unreal’): from Old French fantastique, via medieval Latin from Greek phantastikos, from phantazein ‘make visible’, phantazesthai ‘have visions, imagine’, from phantos ‘visible’ (related to phainein ‘to show’). From the 16th to the 19th centuries the Latinized spelling phantastic was also used.
wiktionary
Borrowed from Middle French fantastique, borrowed from Late Latin phantasticus, borrowed from Ancient Greek φᾰντᾰστῐκός(phantastikós, “imaginary, fantastic; fictional”), ultimately from Proto-Indo-European *bʰeh₂-(“to shine”). Doublet of fantastique.
etymonline
fantastic (adj.)
late 14c., "existing only in imagination, produced by (mental) fantasy," from Old French fantastique (14c.), from Medieval Latin fantasticus, from Late Latin phantasticus "imaginary," from Greek phantastikos "able to imagine," from phantazein "make visible" (middle voice phantazesthai "picture to oneself"); see phantasm. Trivial sense of "wonderful, marvelous" recorded by 1938. Old French had a different adjective form, fantasieus "weird; insane; make-believe." Medieval Latin also used fantasticus as a noun, "a lunatic," and Shakespeare and his contemporaries had it in Italian form fantastico "one who acts ridiculously."
