a word, phrase, pronunciation, or habit that distinguishes who is or isn’t part of a particular group; a common slogan or belief that many think is not valid
—My grandfather’s generation still believes the old shibboleth that “Early to bed and early to rise makes a man healthy, wealthy, and wise.”

Moses died before the Israelites entered the Promised Land, and Joshua took over as their leader. He then led the people into Canaan, where they fought with the residents of the area, taking control of the land. These battles lasted for many generations, and during this time, the Israelites even fought amongst themselves. When the Israelite were led by the judge Jephthah, he led the men of Gilaed in defeat of the Ammonite tribe. The Jews of Ephraim crossed the Jordan River and confronted Jephthah because they were angry with him for not asking for their help in the battle. They threatened the Gileadites, and Jephthah responded by gathering his men and fighting against the men of Ephraim. When the Ehpraimites tried to escape by crossing back over the Jordan, the Gileadites stopped them—but they could not identify them by sight. Instead they had to listen for their accents:

The Gileadites captured the fords of the Jordan River opposite Ephraim. Whenever an Ephraimite fugitive said, “Let me cross over,” the men of Gilead asked him, “Are you an Ephraimite?” If he said, “No,” then they said to him, “Say ‘Shibboleth!’” If he said, “Sibboleth” (and could not pronounce the word correctly), they grabbed him and executed him right there at the fords of the Jordan. On that day forty-two thousand Ephraimites fell dead. (Judges 12:5,6)

The meaning of the Hebrew word shibboleth is “a flowing stream, an ear or head of grain, or branches,” but the meaning was not important—only that the Ephraimites could not pronounce the sh sound.