Massacre
late 16th century: from French, of unknown origin.
wiktionary
1580, from Middle French massacre, from Old French macacre, marcacre, macecre, macecle(“slaughterhouse, butchery”), usually thought to be deverbal from Old French macecrer, macecler(“to slaughter”), though the noun seems to be attested somewhat earlier. It is also found in Medieval Latin mazacrium(“massacre, slaughter, killing”, also “the head of a newly killed stag”). Further origin disputed:
etymonline
massacre (v.)
"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.
massacre (n.)
"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."
