Extraordinarily eccentric or bizarre; wildly imaginative or incredible—an idiom for something utterly outlandish.
彼の発明は奇想天外で、最初は誰も信じなかった。
His invention was so outlandish that at first no one believed it.
作家の奇想天外なアイデアがこの小説を魅力的にしている。
The writer's fantastical ideas make this novel compelling.
舞台演出は奇想天外な演出で観客を驚かせた。
The stage production surprised the audience with its bizarre staging.