massacre vs slaughter

massacre and slaughter both are nouns.

Word	Noun	Adjective	Verb	Adverb
massacre	Yes	No	Yes	No
slaughter	Yes	No	Yes	No

As nouns, massacre and slaughter are synonyms defined as:

Other synonyms of massacre include butchery, carnage, mass murder.

As verbs, massacre and slaughter are synonyms defined as:

Other synonyms of massacre include mow down.

massacre (noun)	slaughter (noun)
the savage and excessive killing of many people	the killing of animals (as for food)
	the savage and excessive killing of many people
	a sound defeat

massacre (verb)	slaughter (verb)
kill a large number of people indiscriminately	kill a large number of people indiscriminately
	kill (animals) usually for food consumption