1. to deny the existence or truth of something
2. to make ineffective or void; to nullify

Examples

• The witness testimony negated the defendant’s alibi.
• Her poor performance negated all her previous achievements.
• The new evidence negates the original theory.
• One mistake can negate hours of careful work.
• The contract clause negates any warranty claims.
• His actions negate his words of apology.
• The storm negated our plans for a picnic.