late 13c., wenche "girl or young woman," shortened from wenchel "child" (12c.), from Old English wencel, probably related to wancol "unsteady, fickle, weak," and cognate with Old Norse vakr "child, weak person," Old High German wanchal "fickle." The word degenerated through being used in reference to servant girls, and by mid-14c. was being used in a sense of "woman of loose morals, mistress."
The wenche is nat dead, but slepith. [Wyclif, Matt. ix:24, c.1380]
"to associate with common women," 1590s, from wench (n.). Related: Wenched; wenching.