An absolute certainty; an easy success. Unlike the meaning of this cliché, the etymology is uncertain. It originated in America in the late nineteenth century and may refer to (l) the cinch that holds a horse’s saddle in place, which, if well fastened, makes it easier for the rider to win a race; or (2), more likely, to plumbing, where a lead pipe is fastened with a steel band to another pipe or fixture, making for a very secure joint. O. Henry used the term in a short story published in 1907 (The Sphinx Apple): “An engagement ain’t always a lead-pipe cinch.”