Merriam-Webster's Collegiate® Dictionary, 11th Edition
MARE
I. noun
Etymology: Middle English, from Old English; akin to Old High German mara incubus, Serbo-Croatian mora nightmare Date: before 12th century an evil preternatural being causing nightmares,
II. noun
Etymology: Middle English, from Old English mere; akin to Old High German merha mare, Old English mearh horse, Welsh march Date: before 12th century a female horse or other equine animal especially when fully mature or of breeding age,
III. noun (plural maria; also mares) see: marine
Date: 1860
any of several mostly flat dark areas of considerable extent on the surface of the moon or Mars