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fantastic

adjective

conceived or appearing as if conceived by an unrestrained imagination; odd and remarkable; bizarre; grotesque: fantastic rock formations; fantastic designs.
fanciful or capricious, as persons or their ideas or actions: We never know what that fantastic creature will say next.
imaginary or groundless in not being based on reality; foolish or irrational: fantastic fears.
extravagantly fanciful; marvelous.
incredibly great or extreme; exorbitant: to spend fantastic sums of money.
highly unrealistic or impractical; outlandish: a fantastic scheme to make a million dollars betting on horse races.
Informal. extraordinarily good: a fantastic musical.

adjective Also: fantastical

strange, weird, or fanciful in appearance, conception, etc
created in the mind; illusory
extravagantly fanciful; unrealisticfantastic plans
incredible or preposterous; absurda fantastic verdict
informal very large or extreme; greata fantastic fortune; he suffered fantastic pain
informal very good; excellent
of, given to, or characterized by fantasy
not constant; capricious; fitfulgiven to fantastic moods

noun

archaic a person who dresses or behaves eccentrically

adj.

late 14c., “existing only in imagination,” from Middle 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.