carnage vs mass murder

carnage and mass murder both are nouns.

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

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

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

Other synonyms of carnage include butchery, massacre, slaughter.

carnage (noun)	mass murder (noun)
the savage and excessive killing of many people	the savage and excessive killing of many people