Definition of "clencher" [clencher]

• One who clenches, or that which is used for clenching, as a cramp or piece of iron bent down to fasten anything. (noun)
• A tool used for clenching or bending over the point of a nail, to prevent its withdrawal. (noun)
• A retort or reply so decisive as to close a controversy; an unanswerable argument: as, the bishop's letter is a clencher. (noun)

The Century Dictionary (Public Domain)

• "The real clencher is whether the characters/story ring true."
• "The clencher was the store clerk's reference to the year of the dragon."
• "This is so late, but I have to tell you as a fellow teeth-clencher -- do wear your bite guard at night."