The Collaborative International Dictionary of English v.0.48:

Envenom \En*ven"om\, v. t. [imp. & p. p. Envenomed; p. pr. &
   vb. n. Envenoming.] [OE. envenimen, F. envenimer; pref. en-
   (L. in) + F. venin poison. See Venom.]
   1. To taint or impregnate with venom, or any substance
      noxious to life; to poison; to render dangerous or deadly
      by poison, as food, drink, a weapon; as, envenomed meat,
      wine, or arrow; also, to poison (a person) by impregnating
      with venom.
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            Alcides . . . felt the envenomed robe. --Milton.
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            O, what a world is this, when what is comely
            Envenoms him that bears it!           --Shak.
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   2. To taint or impregnate with bitterness, malice, or hatred;
      to imbue as with venom; to imbitter.
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            The envenomed tongue of calumny.      --Smollett.
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            On the question of slavery opinion has of late years
            been peculiarly envenomed.            --Sir G. C.
                                                  Lewis.
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WordNet (r) 3.0 (2006):

envenom
    v 1: cause to be bitter or resentful; "These injustices
         embittered her even more" [syn: embitter, envenom,
         acerbate]
    2: add poison to; "Her husband poisoned her drink in order to
       kill her" [syn: poison, envenom]

Moby Thesaurus II by Grady Ward, 1.0:

70 Moby Thesaurus words for "envenom":
   abuse, acerbate, afflict, aggravate, aggrieve, alienate,
   antagonize, befoul, bewitch, bitter, blight, condemn, corrupt,
   crucify, curse, damage, defile, deprave, despoil, destroy,
   disadvantage, disserve, distress, do a mischief, do evil, do ill,
   do wrong, do wrong by, doom, embitter, empoison, estrange,
   exacerbate, get into trouble, harass, harm, heat up, hex, hurt,
   impair, infect, infuriate, injure, jinx, madden, maltreat, menace,
   mistreat, molest, outrage, persecute, play havoc with,
   play hob with, poison, pollute, prejudice, provoke, savage, scathe,
   set against, set at odds, sour, taint, threaten, torment, torture,
   violate, wound, wreak havoc on, wrong