Source : Webster's Revised Unabridged Dictionary (1913)

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
   {viciate}.]
   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
            delusion.                             --South.

            Without care it may be used to vitiate our minds.
                                                  --Burke.

            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.

Source : WordNet®

vitiate
     v 1: corrupt morally or by intemperance or sensuality; "debauch
          the young people with wine and women"; "Socrates was
          accused of corrupting young men"; "Do school counselors
          subvert young children?"; "corrupt the morals" [syn: {corrupt},
           {pervert}, {subvert}, {demoralize}, {demoralise}, {debauch},
           {debase}, {profane}, {deprave}, {misdirect}]
     2: make imperfect; "nothing marred her beauty" [syn: {mar}, {impair},
         {spoil}, {deflower}]
     3: take away the legal force of or render ineffective;
        "invalidateas a contract" [syn: {invalidate}, {void}]
        [ant: {validate}]