mortal lock
n.— Note: A cinch, an odds-on favorite, a guaranteed thing or event. «It is a sure bet—a mortal lock as they say in the business— that if Robespierre was around today, we would be standing knee-deep in decapitations.» —“Five Things: Who Will Punish the Bankers?” by Kevin Depew Minyanville (New York) Apr. 6, 2009. (source: Double-Tongued Dictionary)
Further reading
The expression If you don’t chance your arm, you won’t break your neck makes use of the sense of break your neck meaning “to go all out.” The break your neck part may refer to having success from giving all your effort. Chance your arm, meaning...
Barbara Kingsolver’s book Demon Copperhead is a retelling of Charles Dickens’ David Copperfield set in today’s Appalachia. Martha shares memories of a long-ago visit to Kingsolver’s family farm in Virginia, where they discussed many of the same...