Make something invalid, ineffective or faulty; negate; morally degrade or debase something.
Currently, section 61R of the Crimes Act 1900 provides a list of factors that might vitiate or negate consent, including mistaken belief as to the identity of the other person, as to marriage, or as to medical or hygienic purposes or as a result of threats or terror.
John Hatzistergos, NSW Hansard, 7 November 2007. NSW Hansard
This magazine has been consistent in thinking the Prime Minister was either lying or exaggerating about the WMD. But that did not entirely vitiate the case for war.
Unattributed (Leader), The Spectator, 17 December 2005. The Spectator
True, the larger number of the world's inhabitants have remained deaf to the preaching of the true religion; but that does not vitiate the fact that the Gospel HAS been preached 'for a witness' to all unbelievers from the Papist to the Zulu.
Words penned for a sermon by the character Mr Bodiham in Crome Yellow, by Aldous Huxley. Amazon
They eschew the hand-me-down picturesque conventions that vitiate most "self-taught" painting.