From Longman Dictionary of Contemporary Englishmaremare /meə $ mer/ noun [countable] 1 HBAa female horse or donkey → stallion, filly2 → mare’s nest3 British English spoken informal if someone is having a mare, things are going very badly for them at the moment. It is short for nightmare The Arsenal goalkeeper had a mare in the first half.
Examples from the Corpus
mare• Except in the case of the stallion deliberately herding his mares, this is not a question of dominance or bullying.• I rather gather Geoffrey, my youngest, has got a nice mare showing.• Recruit sought: Cleveland Police are looking for an unusual recruit a horse following the retirement of ten-year-old mare Gellerdale.• The wood was only a hundred paces away, but the sweat-streaked mare was blown and slowing.• And the mare, as if finally understanding, begins to strain, tosses her head wildly, pulls at the reins.• The mare struggles, writhes, strains.Origin mare Old English mere 