What is the meaning of strike down?

verb

• Declare null and void; make ineffective.
  • usage: "Cancel the election results"; "strike down a law"
  • synonyms: cancel
• Cause to die, especially suddenly.
  • usage: "The disease struck down many young men in the village"
• Cause to fall by or as if by delivering a blow.
  • usage: "strike down a tree"; "Lightning struck down the hikers"
  • synonyms: fell, drop, cut down