nightmare

American  

[nahyt-mair] / ˈnaɪtˌmɛər /

noun

1. a terrifying dream in which the dreamer experiences feelings of helplessness, extreme anxiety, sorrow, etc.

   Synonyms:

   phantasmagoria

2. a condition, thought, or experience suggestive of a nightmare.

   the nightmare of his years in prison.

3. (formerly) a monster or evil spirit believed to oppress persons during sleep.

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nightmare British  

/ ˈnaɪtˌmɛə /

noun

1. a terrifying or deeply distressing dream

2. 1. an event or condition resembling a terrifying dream

      the nightmare of shipwreck

   2. ( as modifier )

      a nightmare drive

3. a thing that is feared

4. (formerly) an evil spirit supposed to harass or suffocate sleeping people

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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."

Related Words

See dream.

Other Word Forms

• nightmarish adjective
• nightmarishly adverb
• nightmarishness noun

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

And I was like 'oh my god, this is just a nightmare.

From BBC • Apr. 18, 2026

For an artist like Lori, who works part-time at a Chinese food truck while painting and writing art criticism on the side, the job is both a dream and a nightmare.

From Salon • Apr. 17, 2026

The most shocking thing about Wembanyama’s dream season is that, this time a year ago, the Spurs were suffering through an absolute nightmare.

From The Wall Street Journal • Apr. 16, 2026

Here’s a nightmare scenario that might scare people into thinking hard about who they are hiring: One woman is fighting a $328,000 tax bill because her accountant improperly claimed deductions behind her back.

From MarketWatch • Apr. 9, 2026

When I was a little kid going through my nightmare phase—a giant fish was always trying to eat me—I would crawl into bed with my parents.

From "South of Somewhere" by Kalena Miller

Related Words

• dream
• fantasy
• hallucination
• horror
• ordeal
• vision