c. 1600, "malignant nature;" 1650s, "state of extreme malevolence, bitter enmity," from malignant + abstract noun suffix -cy. Of diseases, growths, tumors, etc., "virulence, tendency to get worse," from 1680s. In English history, "adherence to the royal party in the time of Cromwell," 1640s, from malignants, a term applied to the royalists by their enemies.
