na-adjective
imaginary; fantastical; fanciful; utopian; visionary
Describes ideas, plans, or stories that are imaginative and not grounded in reality, often with a nuance of being unrealistic or idealistic.
彼の話は空想的すぎて、誰も信じなかった。
His story was too fantastical, and no one believed it.
その小説は空想的な世界を描いている。
That novel depicts a fanciful world.
夢想的 also means 'dreamy' or 'visionary', but 空想的 emphasizes a lack of reality, while 夢想的 focuses more on dream-like qualities.
Derived from 空想 (くうそう, 'fantasy' or 'daydream') + the adjectival suffix 的 (てき, '-like' or '-ish').