Did you know?
Looking at nightmare, you might guess that it is a compound formed from night and mare. If so, your guess is correct. But while the night in nightmare makes sense, the mare part is less obvious. Most English speakers know mare as a word for a female horse or similar equine animal, but the mare of nightmare is a different word, an obsolete one referring to an evil spirit that was once thought to produce feelings of suffocation in people while they slept. By the 14th century the mare was also known as nightmare, and by the late 16th century nightmare was also being applied to the feelings of distress caused by the spirit, and then to frightening or unpleasant dreams.
Synonyms
Examples of nightmare in a Sentence
Dan Cancian, Forbes, 20 Nov. 2024
The phrase encapsulates the unwavering hope of the Cuban people that their decades-long nightmare under Fidel Castro (and now his successors) will one day end because darkness eventually always yields to light.
—Carlos Aguilar, Variety, 19 Nov. 2024
Thanks to McLendon-Covey’s inherent gift for never veering into obnoxiousness, Joyce can be both a nightmare of a supervisor and a caring human being.
—Julie Hinds, Detroit Free Press, 10 Nov. 2024
However, their dreams quickly turn into a nightmare.
—Matt Grobar, Deadline, 5 Nov. 2024
See all Example Sentences for nightmare 
Dictionary Entries Near nightmare
Cite this Entry
“Nightmare.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/nightmare. Accessed 30 Nov. 2024.
Copy CitationKids Definition
nightmare
noun
Middle English nightmare "evil spirit thought to haunt people during sleep," from night "night" and mare "spirit," from Old English mare "evil spirit haunting people in sleep"
Medical Definition
nightmare
noun
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