Is it ensure, insure, or assure?
early 13c., Greek liturgical formula, adopted untranslated into the Latin mass, literally "lord have mercy" (Ps. cxxii:3, Matt. xv:22, xvii:15, etc.). From kyrie, vocative of kyrios "lord, master" (see church) + eleeson, aorist imperative of eleo "I have pity on, show mercy to," from eleos "pity, mercy" (see alms).