mow down vs slaughter

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

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

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

Other synonyms of mow down include massacre.

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

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