Synonyms/Hypernyms (Ordered by Estimated Frequency) of noun nightmare

2 senses of nightmare

Sense 1
nightmare, incubus -- (a situation resembling a terrifying dream)
       => situation -- (a complex or critical or unusual difficulty; "the dangerous situation developed suddenly"; "that's quite a situation"; "no human situation is simple")

Sense 2
nightmare -- (a terrifying or deeply upsetting dream)
       => dream, dreaming -- (a series of mental images and emotions occurring during sleep; "I had a dream about you last night")