discredit

Short definition from Wiktionary

Verb

1. 1
   To harm the good reputation of (a person).
2. 2
   To cause (an idea or piece of evidence) to seem false or unreliable.

Noun

1. 1
   Discrediting or disbelieving.
2. 2
   A person or thing that causes harm to a reputation, as of a person, family, or institution.
3. 3
   The state of being discredited or disbelieved.
4. 4
   A degree of dishonour or disesteem; ill repute; reproach.