noun

• (derogatory, dated) A promiscuous woman; also, a mistress (“the other woman in an extramarital relationship”) or a prostitute.
  "Well, yet at length the houre came that flattered him with grace, / Who all too haſtie hide him ſelfe to his appointed place. / Arrived there, a pretie minx (directed wel before) / Unto a lodging brought this lord, and locked faſt the dore. / When he was ſafe, awaye ſhe went, for joy Alberto hopt, / But ſee, a chaunge! too late he ſpyde he was in priſon popt. / The windowes made of yron barres, the walles of ſtone and clay, / A bed he found, but farre unfit he thought for Venus play."
• (obsolete) A pet dog.
  "And of doggues there ben diuerſe ſortes mo then one: For ther be hariers, or buckhoundes, there by ſpanyels made to the hawke, or for taking of foule, ther be ſhepeherdes curres, there are tye dogges or maſtifes for keepinge of houſes, there ben litle minxes, or pupees that ladies keepe in their chaumbers for eſpecial iewels to playe withall. And ſo, to one demaunding what maner a dogge he, for his part was, he feactely aunſwered and ſaied: when I am hungry I am a litle mynxe ful of play, and when my bealy is full, a maſtife."

verb

• (ambitransitive) Used transitively when followed by it: to behave like a minx, that is, in a flirtatious and impudent manner.
  "[He] knows the dress of every girl he meets— / In fact could cut you out the very plan, / Each article could name, and tell you every shade, / Whether adorning minxing miss or ancient maid!"
• (transitive) To make (someone) like a minx; (intransitive) to become like a minx.
  "Whether you're sipping fine bubbly from a crystal flute while having your nails minxed, or soaking in a heavenly milk bath, a visit to Miss Fox is your ticket to forget your worries and simply indulge."