fan·tas·tic / fanˈtastik/ • adj. 1. imaginative or fanciful; remote from reality: novels capable of mixing fantastic and realistic elements. ∎  of extraordinary size or degree: fantastic reductions. ∎  (of a shape or design) bizarre or exotic: visions of a fantastic, mazelike building.2. inf. extraordinarily good or attractive: your support has been fantastic.DERIVATIVES: fan·tas·ti·cal adj. (in sense 1).fan·tas·ti·cal·ly / -(ə)lē/ adv.

fantastic †imaginary XIV; †imaginative XV; extravagantly fanciful XVI. — (O)F. fantastique — medL. fantasticus, lateL. phantasticus — Gr. phantastikós, f. phantázein make visible, phantázesthai have visions, imagine; cf. next and see -IC.
So fantastical XV. The sp. with ph- was frequent XVII–XVIII.