[ muh-lig-nuhnt ]
/ məˈlɪg nənt /
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disposed to cause harm, suffering, or distress deliberately; feeling or showing ill will or hatred.
very dangerous or harmful in influence or effect.
  1. tending to produce death, as bubonic plague.
  2. (of a tumor) characterized by uncontrolled growth; cancerous, invasive, or metastatic.
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Origin of malignant

1535–45; <Late Latin malignant- (stem of malignāns), present participle of malignāre to act maliciously. See malign, -ant


Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023


What’s the difference between malignant and benign?

In a medical context, the word malignant is used to describe harmful masses or tumors that are cancerous and that grow and spread disease. The word benign is the opposite—it’s used to describe masses or tumors that are not cancerous (those that do not spread disease to other parts of the body).

Both words are sometimes also used in general ways. Malignant can mean harmful or intended or intending to cause harm, while benign can mean kind, favorable, or gracious.

The best clue to help remember their meanings is the prefix mal-, which means “bad” and shows up in a lot of other negative words, such as malfunction, malpractice, malicious, and maleficent.

Here’s an example of malignant and benign used correctly in the same sentence.

Example: She was afraid the lump was a malignant tumor, but it turned out to be a benign cyst—totally harmless.

Want to learn more? Read the full breakdown of the difference between malignant and benign.

Quiz yourself on malignant vs. benign!

Should malignant or benign be used in the following sentence?

I can assure you that my intentions are completely _____—I mean no harm.

How to use malignant in a sentence

British Dictionary definitions for malignant

/ (məˈlɪɡnənt) /

having or showing desire to harm others
tending to cause great harm; injurious
pathol (of a tumour) uncontrollable or resistant to therapy; rapidly spreading
history (in the English Civil War) a Parliamentarian term for a royalist (def. 1)

Derived forms of malignant

malignantly, adverb

Word Origin for malignant

C16: from Late Latin malīgnāre to behave spitefully, from Latin malīgnus malign
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for malignant

[ mə-lĭgnənt ]

Tending to have a destructive clinical course, as a malignant illness.
Relating to cancer cells that are invasive and tend to metastasize. Malignant tumor cells are histologically more primitive than normal tissue. Compare benign.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Cultural definitions for malignant


A descriptive term for things or conditions that threaten life or well-being. Malignant is the opposite of benign.

notes for malignant

The term malignant is used in describing cancerous tumors (see cancer) because such growths are a threat to the health of the individual.

notes for malignant

The term is often used in a general way to denote something that is both destructive and fast growing: “The malignant growth of the suburbs is destroying the landscape.”
The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.