Word Origin & History
mare"female horse," O.E. mere (Mercian), myre (W.Saxon), fem. of O.E. mearh "horse," from P.Gmc. *markhjon (cf. O.S. meriha, O.N. merr, O.Fris. merrie, Ger. Mähre "mare"), said to be of Gaulish origin (cf. Ir. and Gael. marc, Welsh march, Bret. marh "horse"). No known cognates beyond Gmc. and Celtic.
As the name of a throw in wrestling, it is attested from c.1600. Mare's nest "illusory discovery, excitement over something which does not exist" is from 1610s.
mare"broad, dark areas of the moon," 1765, from L. mare "sea" (see
marine), applied to lunar features by Galileo and used in 17c. Latin works. They originally were thought to be actual seas.