A shibboleth (ˈʃɪbəlɛθ,_-ɪθ; šībbōleṯ) is any custom or tradition, usually a choice of phrasing or even a single word, that distinguishes one group of people from another. Shibboleths have been used throughout history in many societies as passwords, simple ways of self-identification, signaling loyalty and affinity, maintaining traditional segregation, or protecting from real or perceived threats.
The term originates from the Hebrew word shibbólet (), which means the part of a plant containing grain, such as the head of a stalk of wheat or rye; or less commonly (but arguably more appropriately) "flood, torrent".
The modern use derives from an account in the Hebrew Bible, in which pronunciation of this word was used to distinguish Ephraimites, whose dialect used a differently sounding first consonant. The difference concerns the Hebrew letter shin, which is now pronounced as [ʃ] (as in shoe). In the Book of Judges, chapter 12, after the inhabitants of Gilead under the command of Jephthah inflicted a military defeat upon the invading tribe of Ephraim (around 1370–1070 BCE), the surviving Ephraimites tried to cross the River Jordan back into their home territory, but the Gileadites secured the river's fords to stop them. To identify and kill these Ephraimites, the Gileadites told each suspected survivor to say the word shibboleth. The Ephraimite dialect resulted in a pronunciation that, to Gileadites, sounded like sibboleth. In Judges 12:5–6 in the King James Bible, the anecdote appears thus (with the word already in its current English spelling):
And the Gileadites took the passages of Jordan before the Ephraimites: and it was so, that when those Ephraimites which were escaped said, Let me go over; that the men of Gilead said unto him, Art thou an Ephraimite? If he said, Nay;
Then said they unto him, Say now Shibboleth: and he said Sibboleth: for he could not frame to pronounce it right. Then they took him, and slew him at the passages of Jordan: and there fell at that time of the Ephraimites forty and two thousand.