Vitiate – Spoil or impair the quality or efficiency of something; make it worse
The fish he ate (vitiate) had been spoiled. He felt bad and he was getting worse
Examples of vitiate in a sentence
You made a good decision, so don’t vitiate it by boasting about your success.
When peers and bullies apply pressure, it can vitiate the moral character of young people.
A single word may vitiate a contract.