Synonyms of nightmarish

1 Syllable

dire, grim

2 Syllables

ghoulish, grisly, dreamy, horrid, eerie, scary, fearful, creepier, morbid, moony, dreadful, ghastly, dreamier, awful, spooky, hellish, creepy, chilling

3 Syllables

direful, alarming, terrible, ominous, disquieting, fearsome, terrifying, traumatic, macabre, horrible, petrifying, unnerving, hair-raising, unearthly, bloodcurdling, horrifying

5 Syllables

introvertive, hyperphysical

6 Syllables

phantasmagorical