The Collaborative International Dictionary of English v.0.48:
Vitiate \Vi"ti*ate\, v. t. [imp. & p. p. Vitiated; p. pr. &
vb. n. Vitiating.] [L. vitiatus, p. p. vitiare to vitiate,
fr. vitium a fault, vice. See Vice a fault.] [Written also
1. To make vicious, faulty, or imperfect; to render
defective; to injure the substance or qualities of; to
impair; to contaminate; to spoil; as, exaggeration
vitiates a style of writing; sewer gas vitiates the air.
A will vitiated and growth out of love with the
truth disposes the understanding to error and
Without care it may be used to vitiate our minds.
This undistinguishing complaisance will vitiate the
taste of readers. --Garth.
2. To cause to fail of effect, either wholly or in part; to
make void; to destroy, as the validity or binding force of
an instrument or transaction; to annul; as, any undue
influence exerted on a jury vitiates their verdict; fraud
vitiates a contract.