nightmareEnglishOxford American Thesaurusnightmare noun 1 she had woken from a nightmare: bad dream, night terrors; archaic incubus; rare ephialtes. 2 the long journey home was a nightmare | paperwork is most farmers' nightmare: ordeal, horror, torment, trial; burden, curse, bane, bogey, pet hate, dread, phobia; hell, purgatory, misery, agony, torture, murder; French bête noire.