take French leave

verb2

1. •
   (informal, old-fashioned) To leave quietly and unnoticed, without asking for permission or informing anyone; to slip out.

   • As for Ditton, after all his courting, and his compliment, he stole avvay an Irishman's bride, and took a French leave of me and his master; […] — 1771
2. •
   (informal, old-fashioned) To desert or be temporarily absent from duty or service without permission; to go absent without leave (AWOL).