A family member or a friend is leaving for a trip? Instead of saying Au revoir! (goodbye) or Bon voyage! (Have a good trip) you can say Bon vent! This expression was primarily used for sailors leaving for a very long trip across the seas. Their families were wishing them a bon vent (literally a good wind) that would make their journey pleasant and peaceful. By extension, it became commonly used to say goodbye.
Bon vent!
French with Valerie 