mass murder vs slaughter

mass murder and slaughter both are nouns.

Word	Noun	Adjective	Verb	Adverb
mass murder	Yes	No	No	No
slaughter	Yes	No	Yes	No

As nouns, mass murder and slaughter are synonyms defined as:

mass murder and slaughter: the savage and excessive killing of many people

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

mass murder (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

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