There is no objective definition of what constitutes a "massacre". Various international organisations have proposed a formal definition of the term "crimes against humanity", which would however include incidents of persecution or abuse that do not result in deaths. Conversely, a "massacre" is not necessarily a "crime against humanity". Other terms with overlapping scope include war crime, pogrom, and mass murder.
The modern definition of massacre as "indiscriminate slaughter, carnage", and the subsequent verb of this form, derive from late 16th century Middle French, evolved from Middle French "macacre, macecle" meaning "slaughterhouse, butchery." Further origins are dubious, though may be related to Latin macellum "provisions store, butcher shop."
The Middle French word macecre "butchery, carnage" is first recorded in the late 11th century. Its primary use remained the context of animal slaughter (in hunting terminology referring to the head of a stag) well into the 18th century. The use of macecre "butchery" of the mass killing of people dates to the 12th century, implying people being "slaughtered like animals". The term did not necessarily imply a large number of victims, e.g. Fénelon in Dialogue des Morts (1712) uses l'horride massacre de Blois ("the horrid massacre at Blois") of the assassination of Henry I, Duke of Guise (1588), while Boileau, Satires XI (1698) has L'Europe fut un champ de massacre et d'horreur "Europe was a field of massacre and horror" of the European wars of religion.
The French word is loaned into English in the 1580s, specifically in the sense "indiscriminate slaughter of a large number of people". It is used in reference to St. Bartholomew's Day massacre in The Massacre at Paris by Christopher Marlow. The term is again used in 1695 for the Sicilian Vespers of 1281, called "that famous Massacre of the French in Sicily" in the English translation of De quattuor monarchiis by Johannes Sleidanus (1556), translating illa memorabilis Gallorum clades per Siciliam, i.e. massacre is here used as the translation of Latin clades "hammering, breaking; destruction". The term's use in historiography was popularized by Gibbon's History of the Decline and Fall of the Roman Empire (1781–1789), who used e.g. "massacre of the Latins" of the killing of Roman Catholics in Constantinople in 1182.
An early use in the propagandistic portrayal of current events was the "Boston Massacre" of 1770, which was employed to build support for the American Revolution. A pamphlet with the title A short narrative of the horrid massacre in Boston, perpetrated in the evening of the fifth day of March, 1770, by soldiers of the 29th regiment was printed in Boston still in 1770.