night·mare | \ˈnīt-ˌmer \

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 \ adjective
nightmarishly adverb

Synonyms & Antonyms for nightmare


agony, Gehenna, hell, horror, misery, murder, torment, torture


heaven, paradise

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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

Michael Bublé overcame a parent’s worst nightmare when his son Noah was diagnosed with cancer. Karen Mizoguchi,, "Michael Bublé Opens Up About 'Superhero' Son Noah's Cancer Battle: 'I've Been to Hell'," 8 July 2018 Then there was Eric Thames, remaining the Reds' worst nightmare by hitting a game-turning, three-run homer in the seventh inning off Amir Garrett. Todd Rosiak, Milwaukee Journal Sentinel, "Jesús Aguilar stays hot, Eric Thames torches the Reds once again," 28 June 2018 Impatient and media-savvy millennials have easy access to the kind of ad-blocking services that are the worst nightmare of the business. Steve Donoghue, The Christian Science Monitor, "'Frenemies' is Ken Auletta's brightly readable tour of today's ad business," 20 June 2018 For a writer on deadline, that's the worst nightmare., "World Cup 2018 Daily Podcast: Cristiano Ronaldo Steals the Show Against Spain," 15 June 2018 In short, Elon Musk’s worst nightmare may be more tenable than anyone imagined. Maya Kosoff, The Hive, "Google Tries Being Slightly Less Evil," 8 June 2018 What more indefatigable enemy is there than the family tree, the idea that one’s worst nightmares have been inherited and are doomed to recur from generation to generation? David Sims, The Atlantic, "The Close-to-Home Horror of Hereditary," 7 June 2018 In an effort to end one of the worst PR nightmares in the history of the NFL, rich, old white guys are put their toupees together to solve the kneeling crisis. Mac Engel, star-telegram, "Want to put a stop to kneeling during the national anthem, NFL? Stop playing it | Fort Worth Star-Telegram," 23 May 2018 What sounds like romantic banter to an eavesdropper, could be a nightmare for one or both of the people involved. Taylor Lorenz, The Atlantic, "Stop Live-Tweeting Strangers Flirting," 9 July 2018

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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Phrases Related to nightmare

worst nightmare

Statistics for nightmare

Last Updated

13 Oct 2018

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Time Traveler for nightmare

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

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More Definitions for nightmare



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 \

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 \

Medical Definition of nightmare 

: a frightening or distressing dream that usually awakens the sleeper

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Comments on nightmare

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a generally accepted meaning of a word

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