出典:Wiktionary
From French leave, in supposed reference to the general fashion among the French upper class to leave receptions etc. in the 18th century without always formally announcing their departure to the host or hostess.
take French leave (三人称単数 現在形 takes French leave, 現在分詞 taking French leave, 過去形 took French leave, 過去分詞 taken French leave)