shibboleth (n.)

late 14c., the Hebrew word shibboleth, meaning "flood, stream," also "ear of corn;" in Judges xii.4-6. It was the password used by the Gileadites to distinguish their own men from fleeing Ephraimites, because Ephraimites could not pronounce the -sh- sound. Hence the figurative sense of "watchword" (first recorded 1630s), which evolved by 1862 to "outmoded slogan still adhered to." A similar test-word was cicera "chick pease," used by the Italians to identify the French (who could not pronounce it correctly) during the massacre called the Sicilian Vespers (1282).

During training exercises on Pavuvu and Guadalcanal, the need to improve battlefield security is to be implemented not by a simple password, but by an identification procedure described as "sign and countersign." The ground rules are to sequentially interrogate an unknown friend or foe with the name of an automobile, preferably one with an "L" in its vocalization. The response is to be a cognomen for another automobile uttered in the same manner. This insures the "friend" entering our lines will reply with the correct countersign in a dialect distincly American; call out "Cadiwac" or "Chryswer," and you're dead. [Perry Pollins, "Tales of a Feather Merchant: The World War II Memoir of a Marine Radioman, 2006]