slaughter vs mow down

slaughter is a noun but mow down is not a noun.

Word	Noun	Adjective	Verb	Adverb
slaughter	Yes	No	Yes	No
mow down	No	No	Yes	No

As verbs, slaughter and mow down are synonyms defined as:

Other synonyms of slaughter include massacre.

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

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