The story
From French (adjective) + leave (noun), apparently from a French custom, already recorded in the 18th century, of leaving from receptions or other events without formally announcing one’s departure to the host or hostess. Compare Spanish irse a la francesa and Portuguese sair à francesa (“go in the French manner”) but also the otherwise ubiquitous attribution of this behaviour to the English as with French filer à l’anglaise (“leave in the English manner”), Italian filarsela all'inglese, Polish wyjść po angielsku, etc.
First known use, by meaning
- from mid 18th c. A departure taken quietly and unnoticed, without asking for permission or informing anyone.
Etymology from Wiktionary, CC BY-SA 4.0.