French leaveyoudaoicibaDictYouDict[French leave 词源字典]
"Absence from work or duty without permission", Mid 18th century: said to derive from the French custom of leaving a dinner or ball without saying goodbye to the host or hostess. The phrase was first recorded shortly after the Seven Years War; the equivalent French expression is filer à l'Anglaise, literally 'to escape in the style of the English'.[French leave etymology, French leave origin, 英语词源]