1N-COUNT [usually with poss]情妇 A married man's mistress is a woman who is not his wife and with whom he is having a sexual relationship. 情妇 [old-fashioned]
2N-COUNT [usually n NOUN]女教师 A mistress is a female teacher. 女教师 [British, old-fashioned]
My history mistress was extremely helpful.
教我历史的那位女老师特别乐于助人。
3N-COUNT [usually with poss]女主人 A servant's mistress is the woman that he or she works for. 女主人 [old-fashioned]
It must be really bad, for her to ignore a summons from her mistress!
她居然不听女主人的使唤,实在是太不像话了!
4N-COUNT [usually poss NOUN](狗的)女主人 A dog's mistress is the woman or girl who owns it. (狗的)女主人
The huge wolfhound danced in circles around his mistress.
这条大狼犬围着女主人蹦蹦跳跳地绕圈子。
5N-UNCOUNT [also NOUN in plural, usually NOUNof n]绝对控制…的女人;主宰…的女人 If a woman is mistress of a situation, she has complete control over it. 绝对控制…的女人;主宰…的女人
She had always been mistress of her own destiny.
她总是能够掌握自己的命运。
6N-COUNT [NOUNof n](精通某项活动的)女能手,女行家 If you say that a woman is a mistress of a particular activity, you mean that she is very skilled at it. (精通某项活动的)女能手,女行家
She is a mistress of disguise.
她是伪装的高手。
...another winner from the mistress of historical romance.