neck verse

noun2

1. •
   The verse formerly read to entitle a party to the benefit of clergy, said to be the first verse of the fifty-first Psalm, "Miserere mei," etc.

   • Letter or line know I never a one, Were't my neck-verse at Hairibee — 1805
2. •
   A verse or saying, the utterance of which decides one's fate; a shibboleth.

   • These words, "bread and cheese," were their neck verse or shibboleth to distinguish them; all pronouncing "broad and cause," being presently put to death. — 1655