What does the word vitiate mean?

Usage examples for vitiate

  1. It is as apt to vitiate the system as to protect it." – Barriers Burned Away by E. P. Roe
  2. The fraud by which church, and state substituted that bond made for Saxon swine- herds, who ate boar's heads, lived in unchinked houses and wore brass collars, in the days when Alfred the Great was king, was such as would vitiate any other contract, and must annul even that of marriage; but, granting that it was binding, it must bind both parties, and had been broken by the party of the other part through failure to comply with its requirements. – Half a Century by Jane Grey Cannon Swisshelm
  3. If grief, anger, or excessive joy are able to vitiate secretions, and cause sickness and death, a happy frame of mind, intellectual exertion and moral excellence tend to the perfect health of these secretions. – Studies in the Out-Lying Fields of Psychic Science by Hudson Tuttle