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 The photos of centenarian World War II veterans and an array of world leaders including U.S. President Joe Biden attending the solemn ceremony on Omaha Beach without him were a publicity nightmare. Jill Lawless, The Christian Science Monitor, 11 June 2024 But not all VPNs are created equal—and some could be a privacy nightmare. Kate Irwin, PCMAG, 10 June 2024 The housing boom and crash from almost two decades ago is still a nightmare for homeowners now haunted by zombie mortgages. Catherine Reagor, The Arizona Republic, 7 June 2024 The unsheltered homelessness crisis is a disproportionately and shameful California nightmare. Ethan Deitcher, The Mercury News, 7 June 2024 See all Example Sentences for nightmare 

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 16 Jun. 2024.

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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