"Lead-pipe cinch" is a colloquial phrase that means an absolutely sure thing or a guarantee. The term originated in the early 1900s when lead pipes were commonly used in plumbing and were known for their sturdiness and reliability. Some other synonyms for "lead-pipe cinch" include "dead certainty," "certainty," "surefire," "inevitable," "guaranteed," "inevitable," "assured," "definite," and "unfailingly." These words convey the sense of something that is entirely certain and that can be relied on without reservations. Whether it's a financial investment or a sports game, using these synonyms for "lead-pipe cinch" implies that success is hardly a matter of doubt or question.