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
Literary Hub, 28 Oct. 2025
For years, Billboard has tracked the graveyard smashes, thriller nights and legal nightmares that have sunk their teeth into the KILLboard Rot 100.
—Joe Lynch, Billboard, 27 Oct. 2025
Advertisement Still, how plausible is Bigelow’s tick-tock nightmare?
—Jake Kring-Schreifels, Time, 27 Oct. 2025
King is said to have had nightmares that night — his son running through endless hallways, pursued by a malevolent presence — inspiring the plot of the famous movie.
—Noreen Kompanik, Boston Herald, 26 Oct. 2025
See All Example Sentences for nightmare
Cite this Entry
“Nightmare.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/nightmare. Accessed 29 Oct. 2025.
Copy CitationKids Definition
nightmare
noun
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"
Medical Definition
nightmare
noun
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