vitiate

verb4

1. •
   To spoil, make faulty; to reduce the value, quality, or effectiveness of something.

   • 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. — 1838
2. •
   To debase or morally corrupt.

   • There was excellent blood in his veins—royal stuff; though sadly vitiated, I fear, by the cannibal propensity he nourished in his untutored youth. — 1851
3. •
   To make something ineffective, to invalidate.

   • […]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. — 1734
4. •
   (no longer used) To violate, to rape.