Synonyms for Fantastical:

adj.

all (adjective)
fantastic.
fictitious (adjective)
invented.
imaginary (adjective)
unreal, whimsical, capricious, chimeric, imaginative, chimerical, conceptual, visionary.
marvelous (adjective)
superb, astounding, splendid, sensational, bizarre, incredible, stupendous, glorious, fabulous, prodigious, far-fetched, strange, unbelievable, fantastic, amazing, astonishing, divine.
notional (adjective)
notional.

n.

fancy, imaginative, fanciful, plain, whimsical. changeable, freakish, inconstant, ticklish, volatile, unpredictable, unsteady, mercurial, variable, inconsistent, capricious, unstable, temperamental, erratic, change, uncertain, continue, fickle. fabulous, incredible, amazing, phenomenal, astonishing, good, unbelievable, miraculous, stupendous, prodigious, astounding. fictitious, fictive, fictional, invented, made-up. super, divine, ripping, nifty, dreamy, keen, splendid, hot, great, neat, swell, sensational, superb, groovy, cool, dandy, glorious. fantastical (noun)
strange, grotesque, unreal, antic, unusual, fantastic.

Other synonyms:

chimerical, fictional, conceptual, fanciful, nifty, groovy, invented, far-fetched, fictive, notional, astounding, ripping. chimeric, astonishing, imaginary, fictitious, mercurial, stupendous, amazing, imaginative, unpredictable. inconsistent, made-up, bizarre, prodigious, capricious, inconstant, whimsical, phenomenal, variable, temperamental, fabulous. dandy, freakish, dreamy, fickle, ticklish, miraculous, sensational, volatile, incredible, unbelievable, changeable, visionary. glorious, great, erratic, unstable, unsteady. keen, hot, neat, cool, splendid, divine. uncertain. Other relevant words:
capricious, unpredictable, miraculous, great, sensational, inconsistent, fictive, invented, ripping, conceptual, phenomenal, fantastic, bizarre, hot, fictional, chimerical, fickle, far-fetched, fancy, erratic, unbelievable, astonishing, groovy, dandy, freakish, swell, made-up, chimeric, uncertain, imaginative, temperamental, nifty, astounding, divine, unsteady, notional, superb, unstable, ticklish, changeable, splendid, visionary, stupendous, keen, prodigious, mercurial, whimsical, imaginary, inconstant, amazing, glorious, dreamy, fabulous, neat, super, incredible, fanciful, volatile, variable, fictitious, cool.

Usage examples for fantastical

  1. " That may all very well be," I assented, though I did not believe it, and I found something almost too fantastical in my friend's scheme. – The Standard Household-Effect Company From "Literature and Life" by William Dean Howells
  2. It served two fireplaces, and I proceeded to knock the kinks out of it so it didn'ttie knots in a plumb- line as at first; but, believe me, when it stopped smoking it still whistled, in the most fantastical fashion. – The Siege of the Seven Suitors by Meredith Nicholson