[ nahyt-mair ]
/ ˈnaɪtˌmɛər /
See synonyms for: nightmare / nightmares on


a terrifying dream in which the dreamer experiences feelings of helplessness, extreme anxiety, sorrow, etc.
a condition, thought, or experience suggestive of a nightmare: the nightmare of his years in prison.
(formerly) a monster or evil spirit believed to oppress persons during sleep.


WATCH NOW: The Scary History Behind The Word "Nightmare"

It's dark. You're alone. Was that a footstep? Did something just brush up against you? You fight to get up, but you're stuck ... right on top of you is a horrifying nightmare. Sorry, did you say a nightmare was on top of me?




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Origin of nightmare

Middle English word dating back to 1250–1300; see origin at night, mare2

synonym study for nightmare

1. See dream. Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2021


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.”

Did you know … ?

Nightmares can have many causes—but evil spirits aren’t one of them, despite what Freddy Krueger might say. Stress, eating before bed, medication side effects, and sleep disorders can all cause bad dreams. While children are more likely to have them, half of all adults also report regularly having nightmares.

In fact, nightmares are so familiar (and frightening) to people that the word nightmare has been metaphorically extended to any terrible thought, experience, or situation that resembles a nightmare (e.g., Being lost at sea was a living nightmare).

Worth noting: A night terror is a sudden feeling of extreme fear that awakens a sleeping person, usually during slow-wave sleep, but it is not associated with a dream or nightmare.

The -mare in nightmare doesn’t have anything to do with a mare as in an adult female horse. This homophony hasn’t stopped the card game Magic: The Gathering and other works of pop culture from concocting fictional demonic horse characters that terrify people at night and which go by punny names like Nightmare.

Example sentences from the Web for nightmare

British Dictionary definitions for nightmare

/ (ˈnaɪtˌmɛə) /


a terrifying or deeply distressing dream
  1. an event or condition resembling a terrifying dreamthe nightmare of shipwreck
  2. (as modifier)a nightmare drive
a thing that is feared
(formerly) an evil spirit supposed to harass or suffocate sleeping people

Derived forms of nightmare

nightmarish, adjectivenightmarishly, adverbnightmarishness, noun

Word Origin for nightmare

C13 (meaning: incubus; C16: bad dream): from night + Old English mare, mære evil spirit, from Germanic; compare Old Norse mara incubus, Polish zmora, French cauchemar nightmare
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Medical definitions for nightmare

[ nītmâr′ ]


A dream arousing feelings of intense fear, horror, and distress.
An event or experience that is intensely distressing.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.