The Collaborative International Dictionary of English v.0.48:

Mare \Mare\, n. [AS. mara incubus; akin to OHG. & Icel. mara;
   cf. Pol. mora, Bohem. m[*u]ra.] (Med.)
   Sighing, suffocative panting, intercepted utterance, with a
   sense of pressure across the chest, occurring during sleep;
   the incubus; -- obsolete, except in the compound nightmare.
   [1913 Webster]

         I will ride thee o' nights like the mare. --Shak.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Mare \Mare\ (m[^a]r), n. [OE. mere, AS. mere, myre, fem of AS.
   mearh horse, akin to D. merrie mare, G. m[aum]hre, OHG. marah
   horse, meriha mare, Icel. marr horse, OCelt. marka (Pausan.
   19, 19,4), Ir. marc, W. march. Cf. Marshal.]
   The female of the horse and other equine quadrupeds.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

maria \maria\ n. pl.
   1. (Astron.) Plural form of mare, a dark region of
      considerable extent on the surface of the moon.
      [WordNet 1.5]

   2. (Bot.) A valuable timber tree of Panama.

   Syn: Calophyllum longifolium.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

mare
    n 1: female equine animal [syn: mare, female horse]
    2: a dark region of considerable extent on the surface of the
       moon [syn: mare, maria]