vitiate

1. (transitive) To spoil, make faulty; to reduce the value, quality, or effectiveness of something.Examples: "The least admixture of a lie, -- for example, the taint of vanity, the least attempt to make a good impression, a favorable appearance, -- will instantly vitiate the effect."; "Such diversion as Podson could extort from his isolation was soon vitiated by repetition. He surfed. He sun-baked - with discretion till his skin had peeled and given him a harder cuticle."; "‘Mr Rose,’ says the Physician, ‘this man was brought to us from Russia. Precisely such a case of vitiated judgment as I describe at length in my Treatise on Madness. Mayhap you have read it?’"

2. (transitive) To debase or morally corrupt.Examples: "Dissolute and vitiated alike, they confided in, and ever acted in mutual concert with each other's plans, according to the deep subtleties of their reasonings, which linked them together by some secret spell."; "There was excellent blood in his veins—royal stuff; though sadly vitiated, I fear, by the cannibal propensity he nourished in his untutored youth."; "The robber does not intentionally vitiate people, but the governments, to accomplish their ends, vitiate whole generations from childhood to manhood with false religions and patriotic instruction."

3. (transitive, archaic) To violate, to rape.Examples: "‘Crush the cockatrice,’ he groaned, from his death-cell. ‘I am dead in law’ – but of the girl he denied that he had ‘attempted to vitiate her at Nine years old’; for ‘upon the word of a dying man, both her Eyes did see, and her Hands did act in all that was done’."

4. (transitive) To make something ineffective, to invalidate.Examples: "[…]all the hinges of the animal frame are subverted, every animal function is vitiated; the carcass retains but just life enough to make it capable of suffering."; "He went over his canvases with disgust and anger, unable to see virtue in any one of them. Even his sacred Oyster Girl went back on him. The creature of a vitiated æstheticism, he could only suppose that conceit had played an abominable trick on his eyesight."; "After the trials, Turkey's secular elite was completely vitiated."