Noah Webster's New International Dictionary of the English Language

1. (a.) Disposed to do harm, inflict suffering, or cause distress; malicious; as, a malignant tumor.

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

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

4. (n.) A man of extreme enmity or evil intentions.

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