nullify

Verb

• make ineffective by counterbalancing the effect of
  • Her optimism neutralizes his gloom
    
  • This action will negate the effect of my efforts
    

• show to be invalid

• declare invalid
  • The contract was annulled
    
  • void a plea
    

Related words

• Synonyms: 
  neutralize , neutralise , negate , invalidate , annul , quash , void , avoid
• Antonyms: 
  validate , formalize , formalise