Synonyms for Mow down:

n.

assassinate, take someone's life, strangle, bump off, dispatch. mow down (noun)
massacre, slaughter.

v.

bring down (verb)
level.
cut (verb)
massacre, slaughter, dispatch, raze.
defeat (verb)
decimate, smash, annihilate, demolish.
destroy (verb)
decimate, dismantle, bulldoze, pulverize, exterminate, flatten, desolate, atomize, extirpate, disintegrate, smash, devastate, demolish, abolish, level, destroy, vaporize, raze, tear down, wreck, annihilate, lay waste, eradicate, rip to shreds.
eradicate (verb)
extirpate, exterminate, abolish.
fell (verb)
flatten.
raze (verb)
destroy, wreck, bulldoze, tear down.

Other synonyms:

Other relevant words:
slaughter, massacre, bump off.