What does "malignant" mean?

Additional senses

1. 2.(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.
2. 3.A man of extrems enmity or evil intentions. Hooker.
3. 4.(Eng. Hist.) One of the adherents of Charles L. or Charles LL.; -- so called by the opposite party.