schiboleth

Noun

shibboleth (plural shibboleths)

1. A particular pronunciation or custom that is regarded as distinguishing members of a group from non-members, especially when used as a test.
   • In recent times, the correct treatment of initial h in speech has come to be regarded as a kind of shibboleth of social position.1933, “H”, in Oxford English Dictionary
2. A common or longstanding belief, custom, or catchphrase associated with a particular group, especially one with little current meaning or truth.
   • It's about time we abandoned the bourgeois shibboleth that earning money makes you a better person.