A reduction in the value, or an impairment in the quality of something(noun)
An abolition or abrogation(noun)
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Use "vitiation" in a sentence
"But here again enter error of perspective, and vitiation due to the bias of love."
"Growing numbers of citizens are demanding the independent investigation and prosecution of the members of the Bush administration responsible for the vitiation of fundamental legal principles like habeas corpus and the flagrant violation of both international and domestic laws against torture."
"If the dry skin is a result of pitta vitiation (dry skin in hot weather), then eat light foods that are easy to digest."