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

Europe is a case study in how compassion on a day-to-day basis can turn into a nightmare of difficult-to-assimilate, financially burdensome and culturally disruptive immigrants who individually weren’t perceived to be threats. WSJ, "Consider the Assimilationablity of Refugees," 8 Nov. 2018 To break down exactly what broke down, here's a timeline of how BA2036 turned into a nightmare. Meredith Carey, Condé Nast Traveler, "This Flight Was Delayed for 3 Days—Here's Everything That Went Wrong," 5 Nov. 2018 This turns a weird but seemingly innocuous discovery into a nightmare, fueled by the fundamental fear of your own mind turning against you. Verge Staff, The Verge, "Smart scares for smart people," 31 Oct. 2018 But Ford’s allegations have turned what looked like a political dream for Republicans into a nightmare. Andrew Prokop, Vox, "Why the Senate majority leader keeps pushing so hard to confirm Brett Kavanaugh.," 3 Oct. 2018 But writing those rules sometimes turned into a bureaucratic nightmare — peanut butter’s definition took more than a decade — and regulators eventually stopped setting new standards. Candice Choi, The Seattle Times, "What’s yogurt? Industry wants greater liberty to use term," 25 Sep. 2018 Rivers of flaming jet fuel pour down the holes deep into the bowels of the ship, turning her insides into a living nightmare. John Mccain, Popular Mechanics, "Fire on the Flight Deck," 27 Aug. 2018 For Chris Taylor, a fun afternoon on the beach with his black lab turned into a nightmare. Amanda Garrity, Good Housekeeping, "6-Year-Old Dog Dies From Saltwater Poisoning After a Playful Day at the Beach," 20 July 2018 This puts them at the forefront of any nightmare scenario that is erupting anywhere in the world. Joe Pappalardo, Popular Mechanics, "The C-130J Super Hercules Is Ready for the Worst," 9 Oct. 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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Statistics for nightmare

Last Updated

8 Dec 2018

Look-up Popularity

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

What made you want to look up nightmare? Please tell us where you read or heard it (including the quote, if possible).


a nest or breeding place

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