Malignant describes something very dangerous or harmful, especially a tumor that can spread and become life-threatening. It can also describe a person or force that is deeply evil or destructive.
From Latin 'malignans' meaning 'acting badly' or 'evil in nature', from 'malus' (bad) and a root related to 'genus' (born). It originally described bad or evil will before taking on a specialized medical meaning.
Doctors use 'malignant' as the opposite of 'benign'—think 'bad' versus 'harmless'. Once you know that, medical reports and news stories about cancer suddenly become a lot easier to decode.
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