Synonyms for Strike down:

n.

amendment, codify, criminalize, come in, bring in, decriminalize, backdate, amend, abolish. massacre, bump off, exterminate, strangle, slaughter, dispatch, take someone's life, assassinate. punch someone's lights out, lay out, deck, knock, take down, floor. strike down (noun)
cut down, drop, cancel, fell.

v.

fell (verb)
drop, cut down, floor.
overrule (verb)
cancel.
social (verb)
cancel.

Other synonyms:

deck, floor. take down. lay out. knock. Other relevant words:
deck, floor.