Definition of "neck-verse" [neck-verse]

• A verse in some “Latin book in Gothic black letter” (usually Ps. li. 1), formerly set by the ordinary of a prison before a malefactor claiming benefit of clergy, in order to test his ability to read. If the ordinary or his deputy said “legit ut clericus” (he reads like a clerk or scholar), the malefactor was burned in the hand and set free, thus saving his neck. (noun)
• Hence A verse or phrase on the pronunciation of which one's fate depends; a shibboleth. (noun)

The Century Dictionary (Public Domain)

• "The clerk was held to be a wondrous person in times when the "neck-verse" would save a man from the gallows; but"
• "-- And looks as if he were conning his neck-verse; and in the same dramatist's play of _The Picture_:"
• "Thus the wild borderers, when made prisoners, escaped the halter by pretending to read a verse of the _Miserere_, which they had learnt by heart in case of such an emergency, and called their neck-verse; and "without benefit of clergy" was added to new laws, to prevent education from exempting persons from their power."