1590s, from Middle French débaucher "entice from work or duty," from Old French desbaucher "to lead astray," supposedly literally "to trim (wood) to make a beam" (from bauch "beam," from Frankish balk or some other Germanic source akin to English balk (n.)). A sense of "shaving" something away, perhaps, but the root is also said to be a word meaning "workshop," which gets toward the notion of "to lure someone off the job;" either way the sense evolution is unclear.
[debauch etymology, debauch origin, 英语词源]