Mare

1. An adult female horse.
2. A foolish woman.

noun

A type of evil spirit formerly thought to sit on the chest of a sleeping person; also, the feeling of suffocation felt during sleep, attributed to such a spirit.

1. A demon or monster, thought to plague people while they slept and cause a feeling of suffocation and terror during sleep.
2. Sleep paralysis.
3. A very bad or frightening dream.

   I had a nightmare that I tried to run but could neither move nor breathe.

4. Any bad, miserable, difficult or terrifying situation or experience that arouses anxiety, terror, agony or great displeasure.

   Cleaning up after identity theft can be a nightmare of phone calls and letters.

1. A large, dark plain, which may have the appearance of a sea.
2. On Saturn's moon Titan, a large expanse of what is thought to be liquid hydrocarbons.