a female horse or donkey 母马；母驴 - (British English, informal)
a nightmare (= an experience that is very frightening and unpleasant, or very difficult to deal with) 母马： 一场噩梦（一种令人恐惧，不愉快或难以应对的经历）The journey home was a bit of a mare as all of the trains were delayed. 因为所有的火车都晚点了，所以回家的旅程有点艰难。 I had a complete mare booking tickets for the concert. 我预订音乐会门票的经历真是糟糕透顶。
Word Originnoun Old English mearh ‘horse’, mere ‘mare’, from a Germanic base with cognates in Celtic languages meaning ‘stallion’. The sense ‘male horse’ died out at the end of the Middle English period.
Idioms
a mare’s nest
a discovery that seems interesting but is found to have no value （看似有趣但）毫无价值的发现 a very complicated situation 复杂的形势；变幻莫测的局势 This area of the law is a veritable mare’s nest. 这一法律领域复杂难料。