1560s, in reference to diseases, from Middle French malignant and directly from Late Latin malignantem (nominative malignans) "acting from malice," present participle of malignare "injure maliciously" (see malign (v.)). Earlier in the church malignant "followers of the antichrist," from Latin ecclesiam malignantum in early Church writing, applied by Protestant writers to the Church in Rome (1540s). As an adjective, Middle English used simple malign (early 14c.). Related: Malignantly.
malignant ma·lig·nant (mə-lĭg'nənt)
Threatening to life, as a disease; virulent.
Tending to metastasize; cancerous. Used of a tumor.
A descriptive term for things or conditions that threaten life or well-being. Malignant is the opposite of benign.
Note: The term malignant is used in describing cancerous tumors (see cancer) because such growths are a threat to the health of the individual.
Note: The term is often used in a general way to denote something that is both destructive and fast growing: “The malignant growth of the suburbs is destroying the landscape.”