tumor

American  

[too-mer, tyoo-] / ˈtu mər, ˈtju- /

especially British, tumour

noun

• tumors
  plural

1. a swollen part; swelling; protuberance.

2. an uncontrolled, abnormal, circumscribed growth of cells in any animal or plant tissue; neoplasm.

3. Archaic.

   1. inflated pride; haughtiness.

   2. pompous language; bombast.

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tumor Scientific  

/ to̅o̅′mər /

1. See neoplasm See Note at cancer

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tumor Cultural  

1. An abnormal mass of new tissue growth that serves no function in the body. Tumors are usually classified as benign or malignant and are often caused by cancer.

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Other Word Forms

Derived Forms

• antitumor
  adjective
• antitumoral
  adjective
• nontumorous
  adjective
• tumoral
  adjective
• tumorlike
  adjective
• tumorous
  adjective

Inflected Forms

Nouns

• tumors
  plural

Etymology

Origin of tumor

First recorded in 1535–45; from Latin: “a swelling, swollen state,” equivalent to tum(ēre) “to swell” + -or noun suffix ( see -or ¹)

Explanation

A tumor is a growth — a mass of tissue — that has no function. Tumors can be harmless (benign) or harmful (malignant), but they are never any fun. When a bunch of cells form a new growth in or on an animal, and those cells have no purpose, the result is a tumor. The word tumor comes directly from Latin word for “swelling.” Tumors can be big or small, harmless or harmful. Benign tumors are not a cause for concern, but a malignant tumor is serious and could be cancerous. A doctor must test a tumor to see which kind it is.

Example Sentences

See Examples For:

tumor tumors

The approval marks a major milestone for a type of tumor that can often be a death sentence, and for now RevMed has the field largely to itself.

From The Wall Street Journal ● Aug. 28, 2026

In laboratory experiments, the modified cells successfully infiltrated tumor organoids grown in dishes.

From Science Daily ● Aug. 25, 2026

The researchers briefly exposed natural killer cells to short-lived human epithelial tumor cells that provided a temporary burst of active TGF-b.

From Science Daily ● Aug. 25, 2026

Kidney cancer has fewer mutations to target, while bladder cancer has a more suppressive tumor environment.

From The Wall Street Journal ● Aug. 23, 2026

Each mango-colored puff reminds me that even though I’m not dying of a brain tumor, I still don’t know what’s wrong with me.

From "A Mango-Shaped Space" by Wendy Mass

Together, the RAS mutations drive as much as a third of all human cancers, including most pancreatic tumors.

From The Wall Street Journal ● Aug. 26, 2026

And some of the hardest tumors, such as pancreatic cancer, are notoriously resistant to immune-based treatments.

From The Wall Street Journal ● Aug. 23, 2026

Obesity can interfere with immune function, making it more difficult for the body to respond effectively to tumors.

From Science Daily ● Aug. 22, 2026

The tumors have to be a certain size, for example, according to Christopher.

From MarketWatch ● Aug. 20, 2026

That machine, now turning out radioisotopes and bombarding tumors with neutrons in the Crocker Lab, was the most exquisitely engineered cyclotron in the world, thanks to Brobeck’s painstaking oversight.

From "Big Science" by Michael Hiltzik

Related Words

• Cancer
• carcinoma
• cyst
• lump
• swelling