shibboleth

1. a custom, principle, or belief distinguishing a particular class or group of people, especially a long-standing one regarded as outmoded or no longer important.

   the majority, under the influence of vague nineteenth-century shibboleths, understood him to be associating himself with the doctrine that every nation has a right to be a sovereign state

mid 17th century: from Hebrew šibbōleṯ ‘ear of corn’, used as a test of nationality by its difficult pronunciation (Judg. 12:6).