The Collaborative International Dictionary of English v.0.48:

Venomous \Ven"om*ous\, a. [OE. venemous, venimous, F. venimeux,
   L. venenosus, fr. venenum poison. See Venom, and cf.
   Venenose.]
   1. Full of venom; noxious to animal life; poisonous; as, the
      bite of a serpent may be venomous.
      [1913 Webster]

   2. (Zool.) Having a poison gland or glands for the secretion
      of venom, as certain serpents and insects.
      [1913 Webster]

   3. Noxious; mischievous; malignant; spiteful; as, a venomous
      progeny; a venomous writer.
      [1913 Webster]

   Venomous snake (Zool.), any serpent which has poison glands
      and fangs, whether dangerous to man or not. These serpents
      constitute two tribes, the viperine serpents, or
      Solenoglypha, and the cobralike serpents, or
      Proteroglypha. The former have perforated, erectile fangs
      situated in the front part of the upper jaw, and are
      without ordinary teeth behind the fangs; the latter have
      permanently erect and grooved fangs, with ordinary
      maxillary teeth behind them.
      [1913 Webster] -- Ven"om*ous*ly, adv. --
      Ven"om*ous*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

venomous
    adj 1: extremely poisonous or injurious; producing venom;
           "venomous snakes"; "a virulent insect bite" [syn:
           deadly, venomous, virulent]
    2: marked by deep ill will; deliberately harmful; "poisonous
       hate"; "venomous criticism"; "vicious gossip" [syn:
       poisonous, venomous, vicious]

Moby Thesaurus II by Grady Ward, 1.0:

108 Moby Thesaurus words for "venomous":
   acerbic, acrid, acute, antagonistic, antipathetic, baleful,
   baneful, belligerent, bitter, catching, caustic, clashing,
   colliding, communicable, conflicting, contagious, corroding,
   corrosive, corrupting, corruptive, counterproductive, cutting,
   damaging, dangerous, deadly, deleterious, despiteful, destructive,
   detrimental, disadvantageous, disserviceable, distressing, drastic,
   embittered, envenomed, excessive, exorbitant, extravagant, extreme,
   fierce, full of hate, furious, great, harmful, hateful, hostile,
   hurtful, immoderate, infectious, infective, injurious, intemperate,
   intense, keen, lethal, malefic, maleficent, malevolent, malicious,
   malign, malignant, mean, mephitic, miasmal, miasmatic, miasmic,
   mischievous, noisome, noxious, ominous, outrageous, pernicious,
   pestiferous, pestilential, piercing, poison, poisonous,
   prejudicial, quarrelsome, rancorous, repugnant, rigorous, rough,
   savage, scatheful, set against, severe, sharp, sore, spiteful,
   splenetic, splitting, tough, toxic, toxicant, toxiferous,
   unconscionable, vehement, venenate, veneniferous, venenous,
   vicious, violent, viperish, viperlike, viperous, virulent,
   vitriolic