From Longman Dictionary of Contemporary Englishbe (a/the) mistress of somethingbe (a/the) mistress of somethingCONTROLif a woman is a mistress of something, she is in control of it, highly skilled at it etc → master She appeared to be very much the mistress of the situation. → mistress
Examples from the Corpus
be (a/the) mistress of something• And of course, each girl was the mistress of more than one man.• But if Jacquet de la Guerre was a mistress of the grand gesture, Campra's forte was delicate understatement.• If she married Pogo, she could do exactly as she pleased and she would be mistress of her own home. 