Disposed to inflict suffering or cause distress; having extreme malevolence or enmity; virulently hostile; malicious: as, a malignant heart.Virulently harmful or mischievous; threatening great danger; pernicious in influence or effect.SpecificallyIn astrology, threatening to fortune or life; fateful: as, the malignant aspect of the stars.In pathology, virulent; tending; to produce death; threatening a fatal issue: as, a malignant ulcer; a malignant fever; malignant pustule or scarlet fever.Extremely heinous: as, the malignant nature of sin.Synonyms Malevolent, bitter, rancorous, spiteful, malign. See animosity.n. A person of extreme enmity or evil intentions; an ill-affected person.n. Specifically, in English history, one of the adherents of Charles I. and his son Charles II. during the civil war; a Royalist; a Cavalier: so called by the Roundheads, the opposite party.