rat line
n.— «The Bulgarian secret service, which follows KGB orders without question and which had long-established “rat lines” smuggling spies and arms into Italy and Turkey, was the obvious choice.» —“Did Andropov plot to intimidate Vatican?” by William Safire New York Times Dec. 17, 1982. (source: Double-Tongued Dictionary)
Further reading
If you speak a second or third language, you may remember the first time you dreamed in that new tongue. But does this milestone mean you’re actually fluent? And a couple’s dispute over the word regret: Say you wish you’d been able...