Is it ensure, insure, or assure?
late 12c., from Latin, literally "I believe," first word of the Apostles' and Nicene Creeds, first person singular present indicative of credere "to believe," perhaps from PIE compound *kerd-dhe- "to believe," literally "to put one's heart" (cf. Old Irish cretim, Irish creidim, Welsh credu "I believe," Sanskrit śrad-dhā- "faith"). The nativized form is creed. General sense of "formula or statement of belief" is from 1580s.