"to kill (many beings) indiscriminately," commonly in reference to those who are not in a condition to defend themselves, 1580s, from French massacrer "to slaughter" (16c.), from massacre (n.) "wholesale slaughter, carnage" (see massacre (n.)). Sometimes 17c.-18c. merely "to murder cruelly," without reference to number. Related: Massacred; massacring.
"unnecessary, indiscriminate killing of human beings," sometimes also applied to wholesale slaughter of animals, 1580s, from French massacre "wholesale slaughter, carnage," from Old French macacre, macecle "slaughterhouse; butchery, slaughter," which is of unknown origin; perhaps related to Latin macellum "provisions store, butcher shop," which probably is related to mactāre "to kill, slaughter."