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1. Deprived of legal force
   - invalidated

1. Declare invalid
   "The contract was nullified"
   - invalidate, annul, quash, void, avoid
    
2. Show to be invalid
   - invalidate
    
3. Make ineffective by counterbalancing the effect of
   "Her optimism nullifies his gloom"
   - neutralize, neutralise [Brit], negate

See also: invalid, nullification, nullifier

Type of: cancel, contradict, negate, strike down, weaken

Encyclopedia: Nullify