Impugn (verb)

1. To challenge as false or questionable; to attack or cast doubt on the truth or validity of something.
2. To call into question the honor, integrity, or reputation of someone.
3. To criticize or oppose something or someone in an aggressive or hostile way.

Origin:

From the latin impugnare (to attack, fight against), from in- (in) + pugnare (to fight).

Examples:

1. The lawyer impugned the credibility of the witness.
2. He impugned the motives of the other side.
3. The report impugned the company's accounting practices.
4. The politician's reputation was impugned by the scandal.
5. The critic impugned the artist's work as not being authentic.