Definition of "mare"

mare¹

/mɛə/

noun
plural mares
1. An adult female horse.
  Quotations
  But then I had the [massive] flintlock by me for protection. ¶ […] The linen-press and a chest on the top of it formed, however, a very good gun-carriage; and, thus mounted, aim could be taken out of the window at the old mare feeding in the meadow below by the brook, and a 'bead' could be drawn upon Molly, the dairymaid, kissing the fogger behind the hedge, […].
  1879, R[ichard] J[efferies], chapter 1, in The Amateur Poacher, London: Smith, Elder, & Co., […]
2. (UK, derogatory, slang) A foolish woman.
  Quotations
  The silly mare phoned your mother, talking about applying for a mortgage, and we don't want that, do we?
  2007, Hester Browne, Little Lady, Big Apple

mare²

/mɛə/

noun
plural mares
1. (obsolete or historical) 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.
2. (UK, Ireland, Commonwealth, colloquial) A nightmare; a frustrating or terrible experience.

mare³

/ˈmɑɹ.eɪ/

noun
plural maria
1. (planetology) A large, dark plain, which may have the appearance of a sea, such as those on the Moon
2. (planetology) On Saturn's moon Titan, any of several lakes which are large expanses of what is thought to be liquid hydrocarbons.

mare⁴

noun
plural mares
1. Obsolete form of mayor.
2. Obsolete form of mair.