mare

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A female horse or the female of other equine species.
2. n. Any of the large dark areas on the moon or on Mars or other planets.

Century Dictionary and Cyclopedia

1. n. The female of the horse, or of other species of the genus Equus.
2. n. A few ears of grain left standing and tied together, at which the harvesters throw their sickles till the knot is cut.
3. n. Oppressed sleep; incubus, formerly regarded as an evil spirit of the night that oppresses persons during sleep: now used only in the compound nightmare.
4. An obsolete form of more.
5. n. A sea; specifically, in astronomy, a name for certain dark regions on the surface of the moon which were supposed by Galileo and other early observers to be seas or oceans, and are now regarded as plains; also a name for certain dark regions on the planet Mars.

Wiktionary

1. n. An adult female horse.
2. n. A foolish woman.
3. n. A type of evil spirit thought to sit on the chest of a sleeping person; also the feeling of suffocation felt during sleep; a nightmare.
4. n. (Shortening of term) A nightmare; a frustrating or terrible experience.
5. n. A dark, large circular plain; a “sea”.
6. n. On Saturn's moon Titan, a large expanse of what is thought to be liquid hydrocarbons.

GNU Webster's 1913

1. n. The female of the horse and other equine quadrupeds.
2. n. Sighing, suffocative panting, intercepted utterance, with a sense of pressure across the chest, occurring during sleep; the incubus; -- obsolete, except in the compound nightmare.

WordNet 3.0

1. n. female equine animal
2. n. a dark region of considerable extent on the surface of the moon