malignant

American  

[muh-lig-nuhnt] / məˈlɪg nənt /

adjective

1. disposed to cause harm, suffering, or distress deliberately; feeling or showing ill will or hatred.

   Synonyms:

   malevolent, spiteful

   Antonyms:

   benign

2. very dangerous or harmful in influence or effect.

   Synonyms:

   pernicious, hurtful, perilous

   Antonyms:

   benign

3. Pathology.

   1. tending to produce death, as bubonic plague.

   2. (of a tumor) characterized by uncontrolled growth; cancerous, invasive, or metastatic.

   Antonyms:

   benign

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malignant British  

/ məˈlɪɡnənt /

adjective

1. having or showing desire to harm others

2. tending to cause great harm; injurious

3. pathol (of a tumour) uncontrollable or resistant to therapy; rapidly spreading

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noun

1. history (in the English Civil War) a Parliamentarian term for a royalist

malignant Scientific  

/ mə-lĭg′nənt /

1. Tending to have a destructive clinical course, as a malignant illness.

2. Relating to cancer cells that are invasive and tend to metastasize. Malignant tumor cells are histologically more primitive than normal tissue.

3. Compare benign

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malignant Cultural  

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

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Usage

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.

Discover More

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

Other Word Forms

• malignantly adverb
• nonmalignant adjective
• nonmalignantly adverb
• semimalignant adjective
• semimalignantly adverb
• unmalignant adjective
• unmalignantly adverb

Etymology

Origin of malignant

First recorded in 1535–45; from Late Latin malignant-, stem of malignāns, present participle of malignāre “to act maliciously”; see malign, -ant

Explanation

For something that's very harmful, especially a tumor that's cancerous, use the term malignant. Malignant and its opposite benign are medical terms used to describe a tumor or growth as either cancerous or not respectively. The gn part of both words comes from the Latin word for born, but the word root mal means "evil," while bene means "kind." A malignant tumor grows uncontrollably and spreads to other parts of the body. Less commonly, malignant can also be used to mean "evil or malicious," like when someone has a malignant imagination.

Example Sentences

CAR-T therapy engineers a patient’s own T cells to target and destroy malignant cells, while checkpoint inhibitors remove the immune system’s brakes that tumors use to evade attack.

From The Wall Street Journal • Apr. 19, 2026

In 2023, he told the BBC a mole discovered by his barber during a haircut after a lockdown restriction was found to be malignant melanoma.

From BBC • Apr. 17, 2026

After a week getting steroids and pain medicine at Providence St. John’s Medical Center in Santa Monica, he received the biopsy results: an extremely aggressive malignant mass was blocking blood flow to Duong’s optic nerve.

From Los Angeles Times • Mar. 30, 2026

So everything he is doing now is about legacy, and with a malignant narcissist who knows that he may not be long for this earth, the danger that comes with those realizations is acute.

From Salon • Mar. 29, 2026

It turned out that at the age of thirty-one, Moore had hairy-cell leukemia, a rare and deadly cancer that filled his spleen with malignant blood cells until it bulged like an overfilled inner tube.

From "The Immortal Life of Henrietta Lacks" by Rebecca Skloot

Related Words

• cancerous
• deadly
• destructive
• fatal
• lethal
• mortal