Discredit (verb)

1. Cause (someone or something) to be thought of less favorably.
2. Cause (something) to be distrusted or disbelieved.
3. Damage the reputation of (someone or something).
4. Refuse to believe in the truth or value of (something).

Origin:

Late 16th century: from dis- (expressing negation) + credit.

Examples:

1. The scandal discredited the company.
2. He discredited the witness's testimony.
3. The accusations discredited her.
4. The report discredits the theory.
5. The rumors were designed to discredit him.