cinch / sinch/ • n. 1. inf. an extremely easy task: the program was a cinch to use. ∎ a sure thing; a certainty: he was a cinch to take a prize.2. a girth for a Western saddle or pack.• v. [tr.] 1. secure (a garment) with a belt. ∎ fix (a saddle) securely by means of a girth; girth up (a horse).2. inf. make certain of: his advice cinched her decision to accept the offer.