adj. 25B6; adjective
a fantastic notion : FANCIFUL, extravagant, extraordinary, irrational, wild, absurd, far-fetched, nonsensical, incredible, unbelievable, unthinkable, implausible, improbable, unlikely, doubtful, dubious; strange, peculiar, odd, queer, weird, eccentric, whimsical, capricious; visionary, romantic; informal crazy, cock-eyed, off the wall.
his fantastic accuracy : TREMENDOUS, remarkable, great, terrific, impressive, outstanding, phenomenal.
fantastic shapes : STRANGE, weird, bizarre, outlandish, queer, peculiar, grotesque, freakish, surreal, exotic; elaborate, ornate, intricate.
(informal) a fantastic car : MARVELLOUS, wonderful, sensational, outstanding, superb, excellent, first-rate, first-class, dazzling, out of this world, breathtaking; informal great, terrific, fabulous, fab, mega, super, ace, magic, cracking, cool, wicked, awesome; Brit. informal brilliant, brill, smashing; Austral./NZ informal bonzer; Brit. informal, dated spiffing.
rational, ordinary.