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 (likely a folkloric interpretation of sleep paralysis).
noun A nightmare; a frustrating or terrible experience.
I'm having a complete mare today.
noun A large, dark plain, which may have the appearance of a sea, such as those on the Moon.
noun On Saturn's moon Titan, any of several lakes which are large expanses of what is thought to be liquid hydrocarbons.
Kraken Mare (a lake of liquid hydrocarbons on Titan which is slightly larger than the Caspian Sea)