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]