ma·lig·nant a.
 1. Disposed to do harm, inflict suffering, or cause distress; actuated by extreme malevolence or enmity; virulently inimical; bent on evil; malicious.
    A malignant and a turbaned Turk.   --Shak.
 2. Characterized or caused by evil intentions; pernicious. “Malignant care.”
    Some malignant power upon my life.   --Shak.
    Something deleterious and malignant as his touch.   --Hawthorne.
 3. Med. Tending to produce death; threatening a fatal issue; virulent; as, malignant diphtheria.
 Malignant pustule Med., a very contagious disease produced by infection of subcutaneous tissues with the bacterium Bacillus anthracis.  It is transmitted to man from animals and is characterized by the formation, at the point of reception of the infection, of a vesicle or pustule which first enlarges and then breaks down into an unhealthy ulcer.  It is marked by profound exhaustion and often fatal.  The disease in animals is called charbon; in man it is called cutaneous anthrax, and formerly was sometimes called simply anthrax.

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 An·thrax n.
 1. Med. (a) A carbuncle. (b) A malignant pustule.
 2. Biol. A microscopic, bacterial organism (Bacillus anthracis), resembling transparent rods. [See Illust. under Bacillus.]
 3. An infectious disease of cattle and sheep. It is ascribed to the presence of a rod-shaped gram-positive bacterium (Bacillus anthracis), the spores of which constitute the contagious matter.  It may be transmitted to man by inoculation.  The spleen becomes greatly enlarged and filled with bacteria. Called also splenic fever.

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 An·thrax vac·cine. Veter. A fluid vaccine obtained by growing a bacterium (Bacillus anthracis, formerly Bacterium anthracis) in beef broth. It is used to immunize animals, esp. cattle.

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 Bacillus anthracis
      n : a species of Bacillus that causes anthrax in humans and in
          animals (cattle and swine and sheep and sheep and rabbits
          and mice and guinea pigs); can be used a bioweapon [syn:
          anthrax]