The Collaborative International Dictionary of English v.0.48:

Contaminate \Con*tam"i*nate\ (-n[asl]t), a.
   Contaminated; defiled; polluted; tainted. "Contaminate
   drink." --Daniel.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Contaminate \Con*tam"i*nate\ (k[o^]n*t[a^]m"[i^]*n[=a]t), v. t.
   [imp. & p. p. Contaminated; p. pr. & vb. n.
   Contaminating.] [L. contaminatus, p. p. of contaminare to
   bring into contact, to contaminate, fr. contamen contagion,
   for contagmen; con- + root of tangere to touch. See
   Contact.]
   To soil, stain, or corrupt by contact; to tarnish; to sully;
   to taint; to pollute; to defile.
   [1913 Webster]

         Shall we now
         Contaminate our figures with base bribes? --Shak.
   [1913 Webster]

         I would neither have simplicity imposed upon, nor
         virtue contaminated.                     --Goldsmith.

   Syn: To pollute; defile; sully; taint; tarnish; soil; stain;
        corrupt.
        [1913 Webster]

WordNet (r) 3.0 (2006):

contaminate
    v 1: make impure; "The industrial wastes polluted the lake"
         [syn: pollute, foul, contaminate]
    2: make radioactive by adding radioactive material; "Don't drink
       the water--it's contaminated" [ant: decontaminate]

Moby Thesaurus II by Grady Ward, 1.0:

66 Moby Thesaurus words for "contaminate":
   activate, adulterate, alloy, bastardize, befoul, benasty, canker,
   charge, cheapen, coarsen, confound, corrupt, cut, debase, debauch,
   defile, deflower, degenerate, degrade, denaturalize, denature,
   deprave, desecrate, despoil, devalue, dilute, dirty, disease,
   distort, doctor, doctor up, fortify, foul, harm, infect, injure,
   irradiate, lace, mess, mess up, misuse, nasty, pervert, poison,
   pollute, prostitute, radiumize, ravage, ravish, rot, soil, spike,
   spoil, stain, sully, taint, tamper with, tarnish, twist, ulcerate,
   violate, vitiate, vulgarize, warp, water, water down