1. (

• invalidate ,
• annul ,
• quash ,
• void ,
• avoid ,
• nullify

) declare invalid; "The contract was annulled"; "void a plea" ;

2. (

• invalidate ,
• nullify

) show to be invalid ;

3. (

• neutralize ,
• neutralise ,
• nullify ,
• negate ,

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