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1. Declare invalid
   - annul, quash, void, avoid, nullify
    
2. Make invalid for use
   "invalidate cheques or tickets";
   - cancel
    
3. Show to be invalid
   - nullify
    
4. Take away the legal force of or render ineffective
   "invalidate a contract";
   - void, vitiate

Derived forms: invalidated, invalidates, invalidating

Type of: alter, cancel, change, contradict, mark, modify, negate, score, strike down

Antonym: validate