Definition of "nightmarish"

Meanwhile, the everyday landscape becomes more nightmarish and unmanageable each year.

1994, James Howard Kunstler, The geography of nowhere: the rise and decline of America's man-made landscape, Simon and Schuster, page 10

People sometimes find the idea of buying and selling human bones nightmarish, but Ferry told The Washington Post he doesn’t think of it that way. He says he admires and respects the structure of bones.

2021 October 10, Caroline Anders, “A TikTok bone salesman’s wall of spines reignites ethical debate over selling human remains”, in The Washington Post‎