night·​mare ˈnīt-ˌmer How to pronounce nightmare (audio)
: an evil spirit formerly thought to oppress people during sleep
: a frightening dream that usually awakens the sleeper
: something (such as an experience, situation, or object) having the monstrous character of a nightmare or producing a feeling of anxiety or terror
nightmare adjective
nightmarish adjective
nightmarishly adverb

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.

Examples of nightmare in a Sentence

Mommy, I had a really scary nightmare. The party was a complete nightmare.
Recent Examples on the Web That would be a double-feature nightmare for Chargers fans. Gary Klein, Los Angeles Times, 12 Sep. 2023 With a 6-foot-4, big-bodied frame, Fairweather presents as a mismatch nightmare for opposing defenses. Ainslie Lee |, al, 10 Sep. 2023 Black artists with mainstream aspirations in the United States indeed always come up against this nightmare scenario, rife with ignorance, projection, guilt and a dissatisfying seesaw of overhype and chronic underestimation. Lovia Gyarkye, The Hollywood Reporter, 9 Sep. 2023 Enquirer With his versatility, Highlands senior quarterback Brody Benke can be an absolute nightmare for defenses. Evan Merrill, The Enquirer, 9 Sep. 2023 All new cars today are privacy nightmares on wheels that collect huge amounts of personal information. Peter Weber, The Week, 9 Sep. 2023 Its early, comparatively skillful handling of information — interlacing storylines from different timelines as well as dreams, legends and nightmares — achieved interesting resonances without sacrificing clarity. Lili Loofbourow, Washington Post, 7 Sep. 2023 The only problem is the terrifying red-eyed, midnight black horned demon crawling (and rapping) on her ceiling, illuminated by a snowy TV screen in an homage to another freaky suburban nightmare classic, Poltergeist. Gil Kaufman, Billboard, 1 Sep. 2023 So there are many reasons to keep your feet dry, especially during colder months when the combination of frigid air and moisture is a nightmare. Joel Balsam, Travel + Leisure, 29 Aug. 2023 See More

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'nightmare.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


Middle English nyghte mare, from nyghte night entry 1 + mare mare entry 3

First Known Use

14th century, in the meaning defined at sense 1

Time Traveler
The first known use of nightmare was in the 14th century


Dictionary Entries Near nightmare

Cite this Entry

“Nightmare.” Dictionary, Merriam-Webster, Accessed 1 Oct. 2023.

Kids Definition


night·​mare ˈnīt-ˌma(ə)r How to pronounce nightmare (audio)
: a frightening dream
: a frightening or horrible experience
nightmarish adjective

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"

Word Origin
In the Middle Ages many people believed in a type of evil spirit that was said to haunt people while they slept. Such a demon was known in Old English as a mare. Because it was believed to come in the night, it later became known in Middle English as a nightmare. It was not until the 16th century that the word nightmare came to mean "a frightening dream." This meaning probably came from the belief that such dreams were caused by evil spirits.

Medical Definition


: a frightening or distressing dream that usually awakens the sleeper

More from Merriam-Webster on nightmare

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