Shibboleth

From the Hebrew shibbóleth (meaning "ear of grain" or "torrent"), the word originates in the Book of Judges (12:5-6), where Gileadite soldiers used it as a pronunciation test to identify fleeing Ephraimites at the fords of the Jordan — those who said "sibboleth" instead were killed. The story gave English a word for any marker of group identity; its figurative use dates to at least the 14th century.