Discredit

To damage the reputation or credibility of someone or something; to cause people to doubt the truth or value of something.

Formed by adding the prefix 'dis-' (meaning 'opposite of' or 'away from') to 'credit'. The word 'credit' comes from Latin 'creditum' meaning 'something entrusted' or 'belief', so discredit literally means to take away belief or trust.