/məˈlignənt/
Adjective
1. Harmful, malevolent, injurious. (wiktionary.org)
2. Dangerous to health; characterized by progressive and uncontrolled growth (especially of a tumor). (wordnetweb.princeton.edu)
(Oncology)
1. Harmfully cancerous; as a malignant tumor. (wiktionary.org)
Word origin: From Middle French malignant and directly from Late Latin malignantem (nominative malignans) “acting from malice,” present participle of malignare “injure maliciously.”