nightmare
Americannoun
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a terrifying dream in which the dreamer experiences feelings of helplessness, extreme anxiety, sorrow, etc.
- Synonyms:
- phantasmagoria
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a condition, thought, or experience suggestive of a nightmare.
the nightmare of his years in prison.
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(formerly) a monster or evil spirit believed to oppress persons during sleep.
noun
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a terrifying or deeply distressing dream
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an event or condition resembling a terrifying dream
the nightmare of shipwreck
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( as modifier )
a nightmare drive
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a thing that is feared
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(formerly) an evil spirit supposed to harass or suffocate sleeping people
Usage
Where does the word nightmare come from? Nightmares are scary and unpleasant. But you can rest easy knowing that the fascinating origin of the word nightmare makes it clear humans have been having them for hundreds of years. In Old English, a mare was a kind of evil or cursed spirit. Mares appear in all kinds of folklore, including German and Slavic stories. Mares were said to ride on people's chests at night, causing suffocation and bad dreams. These mares, often female, were known as nightmares (because they came at night). By the 16th century, the word nightmare came to refer to a sensation of suffocation or anxiety during sleep, and now simply a bad dream. While nightmares are terrifying, there is good news: at least most of us don't worry about evil spirits trying to suffocate us in our sleep anymore. The roots of these other words may get a rise—of laughter or surprise—out of you. Run on over to our roundup of them at "Weird Word Origins That Will Make Your Family Laugh."
Synonym Usage
See dream.
Other Word Forms
Derived Forms
Inflected Forms
Nouns
Etymology
Origin of nightmare
Middle English word dating back to 1250–1300; see origin at night, mare 2
Explanation
If you wake with a start after a terrifying dream, you've had a nightmare. A nightmare is not just a bad dream — it's seriously scary or upsetting. You can also use nightmare to describe something terrible that happens during the day. Your run-in with a skunk in your back yard might be a nightmare, for example, or your humiliating experience forgetting your lines in a play. In the late thirteenth century, a nightmare was "an evil female spirit afflicting sleepers with a feeling of suffocation," from the Old English word mare, "incubus or goblin."
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
Appeared in the June 27, 2026, print edition as 'Ohio Campaign Pits Covid Nightmare vs. the American Dream'.
From The Wall Street Journal • Jun. 26, 2026
In 1993 she collaborated again with Burton on "The Nightmare before Christmas."
From Barron's • Jan. 30, 2026
The Canadian was Oscar-nominated for her work on his film Nightmare Alley.
From BBC • Oct. 31, 2025
Side was treated as a leading entrepreneur in the business: In May 2024, she appeared on a panel titled “Challenges in Escrow Management: Nightmare Cases.”
From The Wall Street Journal • Oct. 22, 2025
The blazing blue sky turns gray, then dark, and Nightmare Me thinks it’s the most amazing thing I’ve ever seen.
From "Hello, Universe" by Erin Entrada Kelly
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
