rat line n. a covert path or itinerary used for smuggling, escape, or supply. Etymological Note: This term derives from the tendency of rats to create routes that are out of sight as much as possible, following perimeters and the bases of obstructions. (source: Double-Tongued Dictionary)
Further reading
Mark in Bismarck, North Dakota, spent years as a sailor, and wonders about the term sea painter, meaning “a rope attached to a lifeboat.” Why painter? The word may derive from Middle French pendeur meaning “a kind of rope that...
A resident of Michigan’s scenic Beaver Island shares the term, boodling, which the locals use to denote the social activity of leisurely wandering the island, often with cold fermented beverages. There have been various proposed etymologies...