malignant (adj.)
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.