night·​mare | \ ˈnīt-ˌmer How to pronounce nightmare (audio) \

Definition of nightmare

1 : an evil spirit formerly thought to oppress people during sleep
2 : a frightening dream that usually awakens the sleeper
3 : something (such as an experience, situation, or object) having the monstrous character of a nightmare or producing a feeling of anxiety or terror

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Other Words from nightmare

nightmare adjective
nightmarish \ ˈnīt-​ˌmer-​ish How to pronounce nightmarish (audio) \ adjective
nightmarishly adverb

Synonyms & Antonyms for nightmare



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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 a 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 The nightmare scenario, of course, is that the bug would start to show up in California, the $50 billion-a-year engine of American agriculture, and one of the world’s greatest wineries. Marc Mcandrews, Smithsonian Magazine, "Can Scientists Stop the Plague of the Spotted Lanternfly?," 22 Sep. 2020 PitchBook mobility analyst Asad Hussain describes a nightmare scenario where Waymo develops its own network, Amazon gives free rides to Prime subscribers, and Uber becomes irrelevant. Lizette Chapman,, "Uber Investors Are Pressuring CEO to Revamp the Self-Driving Division," 21 Sep. 2020 The fragments would grow smaller, more numerous, more uniform in direction, resembling a maelstrom of sand—a nightmare scenario that became known as the Kessler syndrome. Raffi Khatchadourian, The New Yorker, "Read More," 21 Sep. 2020 That sounds like a nightmare scenario even without a pandemic. Caroline Delbert, Popular Mechanics, "Was Trump's Indoor Rally a Superspreader Event?," 15 Sep. 2020 Her exploration of humans volunteering to be virus antibody farms is a nightmare scenario that feels a little too possible. Monica Tapiarené By Ken Hogarty,, "Reader fiction: Throughline inspires short fiction by Bay Area residents," 6 Sep. 2020 However, the situation also represents the nightmare scenario of a team experiencing an outbreak in a position group once the season is underway. Eddie Timanus, USA TODAY, "Report: LSU offensive line down to four players due to COVID-19 positives and quarantines," 26 Aug. 2020 Either way, the worst-case consequences are the same: a nightmare scenario in which thousands or millions of Americans who lawfully vote by mail—and are overwhelmingly registered Democrats—are nonetheless disenfranchised. Gilad Edelman, Wired, "Honestly, Just Vote In Person—It’s Safer Than You Think," 17 Aug. 2020 But Ohio State seems committed to considering every possible option before choosing the nightmare scenario. Nathan Baird, cleveland, "Ohio State’s Ryan Day advocates Buckeyes making own schedule if Big Ten cancels football: Is ‘going rogue’ realistic?," 11 Aug. 2020

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'nightmare.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of nightmare

14th century, in the meaning defined at sense 1

History and Etymology for nightmare

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

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Time Traveler for nightmare

Time Traveler

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

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Statistics for nightmare

Last Updated

26 Sep 2020

Cite this Entry

“Nightmare.” Dictionary, Merriam-Webster, Accessed 29 Sep. 2020.

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More Definitions for nightmare


How to pronounce nightmare (audio)

English Language Learners Definition of nightmare

: a dream that frightens a sleeping person : a very bad dream
: a very bad or frightening experience or situation


night·​mare | \ ˈnīt-ˌmer How to pronounce nightmare (audio) \

Kids Definition of nightmare

1 : a frightening dream
2 : a horrible experience

Other Words from nightmare

nightmarish \ ˈnīt-​ˌmer-​ish \ adjective


night·​mare | \ ˈnīt-ˌma(ə)r, -ˌme(ə)r How to pronounce nightmare (audio) \

Medical Definition of nightmare

: a frightening or distressing dream that usually awakens the sleeper

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