1. Deny the truth of
   "His actions negated his promises";
   - contradict, contravene
    
2. (logic) prove negative; show to be false
   "The experiment negated the hypothesis";
   - contradict
    
3. Make ineffective by counterbalancing the effect of
   "This action will negate the effect of my efforts";
   - neutralize, neutralise [Brit], nullify
    
4. Be in contradiction with
   "His actions negated his words";
   - contradict, belie

Derived forms: negating, negates, negated

Type of: demonstrate, depart, deviate, differ, disagree, dissent, diverge, establish, prove, shew [Brit, archaic], show, take issue, vary, weaken

Encyclopedia: Negate