Merriam-Webster Collegiate Dictionary - shibboleth

 noun  Etymology: Hebrew shibboleth stream; from the use of this word in Judges 12:6 as a test to distinguish Gileadites from Ephraimites  Date: 1638  1.  a. a word or saying used by adherents of a party, sect, or belief and usually regarded by others as empty of real meaning the old ~s come rolling off their lips — Joseph Epstein  b. a widely held belief today this book publishing ~ is a myth — L. A. Wood  c. truism, platitude some truth in the ~ that crime does not pay — Lee Rogow  2.  a. a use of language regarded as distinctive of a particular group accent was…a ~ of social class — Vivian Ducat  b. a custom or usage regarded as distinguishing one group from others for most of the well-to-do in the town, dinner was a ~, its hour dividing mankind — Osbert Sitwell