malignant

adj

1. Harmful, malevolent, injurious.

   “malignant temper; malignant revenge; malignant infection”

   “[…]while, I fear, there will be some white ones, unable to forget that, with malignant heart, and deceitful speech, they have strove to hinder it.”

2. Tending to produce death; threatening a fatal issue.

   “malignant diphtheria”

   “a malignant tumor”

   ““[…] the awfully hearty sort of Christmas cards that people do send to other people that they don't know at all well. You know. The kind that have mottoes[…]. And then, when you see [the senders], you probably find that they are the most melancholy old folk with malignant diseases. […]””

noun

1. A deviant; a person who is hostile or destructive to society.

   “As devout Stephen was carried to his burial by devout men, so is it just and equal that malignants should carry malignants […]”

   “A malignant in a position of real power immediately becomes a tyrant.”

2. (derogatory, historical, obsolete)A person who fought for Charles I in the English Civil War.