mara
n. countablen. a bad spirit or demon that people in the past believed caused nightmares. It is where the second half of the word 'nightmare' comes from.
n. a malevolent entity in Germanic and Slavic folklore believed to sit on the chests of sleepers to cause bad dreams or suffocation. Often used in historical or literary contexts to explain the etymology of 'nightmare'.
Old legends tell of a mara that visits people at night.
The painting depicts a mara sitting heavily upon a sleeping woman, illustrating the folklore behind sleep paralysis.
In medieval superstition, the mara was not merely a dream but a physical weight that oppressed the sleeper, a concept that persists linguistically in several European languages.
Commonly appears in discussions of etymology or European folklore.