Vitiate: impairment of legal efficacy that renders an act or instrument voidable due to defects like fraud. Vitiate denotes the impairment or nullification of the legal efficacy of an act or instrument, rendering it void or voidable either wholly or in part; it covers acts that destroy, annul, or cause an instrument to fail of force or effect, and operates where a defect-such as fraud-undermines the binding force of a contract or other legal document.