MALIGNANT

adj. malevolent, malicious, spiteful; harmful; deadly, fatal, likely to cause death (Pathology); cancerous (Pathology)

Malignant (from the Latin roots mal- = "bad" and -genus = "born") is a medical term used to describe a severe and progressively worsening disease. The term is most familiar as a description of cancer. A malignant tumor may be contrasted with a non-cancerous benign tumor in that a malignancy is not self-limited in its growth, is capable of invading into adjacent tissues, and may be capable of spreading to distant tissues (metastasizing), while a benign tumor has none of those properties. Uses of "malignant" in oncology:Malignancy, malignant neoplasm, and malignant tumor are synonymous with cancerMalignant ascitesMalignant transformation
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Adjective
1. dangerous to health; characterized by progressive and uncontrolled growth (especially of a tumor)
(antonym) benign
(similar) cancerous
(classification) pathology
2. extremely malevolent or malicious; "the malignant tongues of gossipers"
(synonym) malevolent
(similar) malign

(n.)
One of the adherents of Charles L. or Charles LL.; -- so called by the opposite party.
  

(n.)
A man of extrems enmity or evil intentions.
  

(a.)
Tending to produce death; threatening a fatal issue; virulent; as, malignant diphtheria.
  

(a.)
Disposed to do harm, inflict suffering, or cause distress; actuated by extreme malevolence or enmity; virulently inimical; bent on evil; malicious.
  

(a.)
Characterized or caused by evil intentions; pernicious.
  

Malignant means to resistant to treatment, or severe (As in "malignant hypertension"). When referring to an abnormal growth it implies a tendency to metastasize. The word malignant comes the Latin combination of mal meaning bad and nascor meaning to be born; malignant literally means born to be bad.