Shibboleth

sabbath? A shibboleth (/ˈʃɪbəlɛθ/[1] or /ˈʃɪbələθ/)[2] is a word, sound, or custom that a person unfamiliar with its significance may not pronounce or perform correctly relative to those who are familiar with it. It is used to identify foreigners or those who do not belong to a particular class or group of people. It also refers to features of language, and particularly to a word or phrase whose pronunciation identifies a speaker as belonging to a particular group. The term originates from the Hebrew word shibbólet (שִׁבֹּלֶת), which literally means the part of a plant containing grains, such as an ear of corn or a stalk of grain[3] or, in different contexts, "stream, torrent".[4][5] The modern usage derives from an account in the Hebrew Bible, in which pronunciation of this word was used to distinguish Ephraimites, whose dialect lacked a /ʃ/ phoneme (as in shoe), from Gileadites whose dialect did include such a phoneme.

Recorded in the Book of Judges, chapter 12, after the inhabitants of Gilead inflicted a military defeat upon the tribe of Ephraim (around 1370–1070 BC), the surviving Ephraimites tried to cross the Jordan River back into their home territory and the Gileadites secured the river's fords to stop them. In order to identify and kill these refugees, the Gileadites put each refugee to a simple test:

   Gilead then cut Ephraim off from the fords of the Jordan, and whenever Ephraimite fugitives said, 'Let me cross,' the men of Gilead would ask, 'Are you an Ephraimite?' If he said, 'No,' they then said, 'Very well, say "Shibboleth" (שבלת).' If anyone said, "Sibboleth" (סבלת), because he could not pronounce it, then they would seize him and kill him by the fords of the Jordan. Forty-two thousand Ephraimites fell on this occasion.
       —Judges 12:5–6, NJB