shibboleth

n. [ Heb. shibbōleth an ear of corn, or a stream, a flood. ] 1. A word which was made the criterion by which to distinguish the Ephraimites from the Gileadites. The Ephraimites, not being able to pronounce sh, called the word sibboleth. See Judges xii. [ 1913 Webster ]

Without reprieve, adjudged to death,
For want of well pronouncing shibboleth. Milton. [ 1913 Webster ]

Also used in an extended sense. [ 1913 Webster ]

The th, with its twofold value, is . . . the shibboleth of foreigners. Earle. [ 1913 Webster ]

2. Hence, the criterion, test, or watchword of a party; a party cry or pet phrase. [ 1913 Webster ]