Is it ensure, insure, or assure?
early 15c., "buy back, ransom," from Middle French redemer "buy back," from Latin redimere (see redemption). Theological sense of "deliver from sin and spiritual death" is from c.1500. Meaning "make amends for" is from 1520s. Sense of "make good" (a promise, obligation, etc.) is from 1840. Related: Redeemed; redeeming.