“Nightmare” Has Nothing to Do with Horses: The Real Meaning of the Nocturnal Mare

The Apparent Meaning

To a modern English speaker, “nightmare” seems to parse cleanly: “night” + “mare” = a night horse. The image is vivid — a wild horse galloping through the darkness of sleep, associated with panic, stampede, the uncontrollable. The word seems to do exactly what it looks like it does. Horses and bad dreams share qualities of wildness, irresistibility, and the sensation of being carried somewhere against your will.

But this reading is wrong, and the true etymology is considerably stranger and more interesting.

The “mare” in “nightmare” is not a horse. It never was. It is a demon.

The Mara: An Ancient Supernatural Figure

Old English “mære” (also written “mara”) was the name for a specific supernatural creature in Germanic folklore: an evil spirit — typically imagined as female — that visited sleeping people at night, sat on their chests, and caused suffocating, terrifying dreams. The creature is documented across Germanic and Scandinavian cultures under related names: German “Mahr” or “Mahr,” Scandinavian “mara,” Old Norse “mara,” and (in a compound borrowed from Flemish into French) “cauchemar” — literally “the trampling mare,” the demon that presses down.

The experience attributed to the “mara” is now understood as sleep paralysis: a documented neurological phenomenon in which a person wakes during REM sleep while their voluntary muscles remain temporarily paralysed — as they normally are during dreaming, to prevent the sleeper from acting out their dreams. The paralysis typically lasts seconds to minutes, but during that time the person is fully conscious, unable to move, and often experiencing vivid hallucinations. A common hallucination during sleep paralysis is the sensation of a figure or presence in the room, and the feeling of a heavy weight pressing on the chest, causing difficulty breathing.

Before scientific understanding of sleep, this experience was universally interpreted as supernatural visitation. Every culture that has described sleep paralysis attributes it to some kind of supernatural pressure: the Germanic “mare,” the Italian “old hag,” the Japanese “kanashibari” (bound in metal), the West African “kokma,” the Caribbean “kokma.” The “mare” of Old English folklore is the Germanic name for what is in fact a cross-cultural neurological experience.

The Two “Mares”: Why the Confusion Exists

Modern English has two words spelled “mare” with completely different origins. The demon “mare” comes from Old English “mære,” from Proto-Germanic *maron — a root reconstructed as referring to supernatural female spirits or crushing entities. The female horse “mare” comes from Old English “mearh” (horse in general), later “miere” / “mere” (specifically female horse), from Proto-Germanic *marhijō — a root meaning horse, cognate with Welsh “march” (horse) and Old Irish “marc” (horse).

These two words happened to converge in spelling in Middle English — both producing “mare” — despite having entirely different origins. This convergence is pure accident, and it is the accident that creates the persistent misconception about nightmares and horses.

The Old English compound “nihtmære” (night-demon) appears in texts from around the 13th century onward, with the modern “nightmare” stabilising in the 16th century. Throughout this history, the “-mare” element consistently refers to the supernatural entity, never to a horse. Chaucer uses “mare” in the supernatural sense in the 14th century; Shakespeare uses “nightmare” in King Lear in 1606 in the same sense.

Across Languages: The Same Creature by Different Names

The survival of the “mare” creature in multiple languages confirms its importance in the pre-scientific understanding of sleep. French “cauchemar” (nightmare) combines the verb “caucher” (to trample, to press upon — related to English “cache”) with “mare” (the same Germanic demon): a nightmare is literally a demon that tramples you while you sleep. The word entered French from Flemish-speaking Walloon dialects of Belgium, where Germanic and Romance languages overlapped.

In German, the creature survives as “Mahr” or “Nachtmahr” (night-mare, in the original sense). In Icelandic, “mara” still means both the creature and, by extension, a nightmare. In Czech and Slovak, “můra” means moth (which flutters at night and was associated with the supernatural) but also retains traces of the nightmare-creature meaning. The creature appears in Norse mythology explicitly as Sleipnir, Odin’s eight-legged horse — but this is a secondary association, where the horse-spirit and the nightmare-spirit traditions merged, not evidence that the original “mare” was equine.

The “Nightmare” Painting

Perhaps the most famous visual representation of the nightmare creature is Henry Fuseli’s 1781 oil painting, simply titled The Nightmare. It shows a woman sprawled unconscious across her bed, a small incubus-like creature squatting on her chest — and, in the background, a horse’s head emerging from the shadows. Fuseli, working in the 18th century, appears to have known that the creature was not a horse, but was also playing with the visual ambiguity between “mare” (demon) and “mare” (horse). The painting is one of the first great depictions of sleep paralysis — and its background horse is a deliberate pun, not an etymological explanation.

The word “nightmare” carries this long, strange history in its two syllables: a night, and a demon that presses on the sleeping chest. Every time the word is used, it invokes a creature from Germanic folklore, a neurological experience that has terrified people across every culture, and the long-forgotten demonology of the Old English world. The horse has nothing to do with it.