Is it ensure, insure, or assure?
1580s, from Middle French massacrer "to slaughter" (16c.), from massacre (n.) "wholesale slaughter, carnage" (see massacre (n.)). Related: Massacred; massacring.
1580s, from Middle French massacre "wholesale slaughter, carnage," from Old French macacre, macecle "slaughterhouse, butchery," of unknown origin; perhaps related to Latin macellum "provisions store, butcher shop."