Source : Webster's Revised Unabridged Dictionary (1913)

Pustule \Pus"tule\ (?; 135), n. [L. pustula, and pusula: cf. F.
   pustule.] (Med.)
   A vesicle or an elevation of the cuticle with an inflamed
   base, containing pus.

   {Malignant pustule}. See under {Malignant}.

Malignant \Ma*lig"nant\, a. [L. malignans, -antis, p. pr. of
   malignare, malignari, to do or make maliciously. See
   {Malign}, and cf. {Benignant}.]
   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.'' --Macaulay.

            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,
      transmitted to man from animals, characterized by the
      formation, at the point of reception of the virus, of a
      vesicle or pustule which first enlarges and then breaks
      down into an unhealthy ulcer. It is marked by profound
      exhaustion and usually fatal. Called also {charbon}, and
      sometimes, improperly, {anthrax}.

Source : WordNet®

malignant pustule
     n : a form of anthrax infection that begins as papule that
         becomes a vesicle and breaks with a discharge of toxins;
         symptoms of septicemia are severe with vomiting and high
         fever and profuse sweating; the infection is often fatal
         [syn: {cutaneous anthrax}]