means A mare is an adult female horse (or female donkey, zebra, or other equine), the counterpart to the stallion.

from Straight out of Old English 'mere,' the female of 'mearh' (horse), with kin across the Germanic family — Old Norse 'merr,' German 'Mähre.' The same root gallops into 'marshal,' which began as a 'horse-servant' (from Frankish 'marah-skalk,' horse-servant) before climbing the ranks to mean a commander. Note the false friend: the 'mare' in 'nightmare' is a wholly different beast — an Old English 'mære,' a crushing demon that sat on sleepers' chests, with no equine connection at all.