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

What has been less clear is how those nerves enter the tumor in the first place.

From Science Daily ● Aug. 17, 2026

Before surgery, Amabile shared that he would undergo a craniotomy, a surgery in which a neurosurgeon temporarily removes a piece of the skull to reach the brain and remove the tumor.

From Los Angeles Times ● Aug. 11, 2026

“We will actually have so much more information once the tumor is removed and they test it and then we can actually create a plan of next steps,” Pitt said on the podcast.

From Los Angeles Times ● Aug. 11, 2026

The outcome changed when researchers stopped fibroblasts inside the tumor from producing C3.

From Science Daily ● Aug. 8, 2026

The doctors suspected that he had been born with the tumor and it had suddenly started to grow.

From "Reaching for the Moon" by Katherine Johnson

Scientists have known for years that many solid tumors contain extensive nerve networks.

From Science Daily ● Aug. 17, 2026

Scientists at Nagoya University in Japan discovered that complement C3 can prevent immune-suppressing cells from building up inside tumors, but only when the protein is produced locally within the tumor.

From Science Daily ● Aug. 8, 2026

The findings, published in Nature Communications, suggest that reproducing this local effect could benefit patients whose tumors do not produce enough C3 naturally.

From Science Daily ● Aug. 8, 2026

Small trials have given high-dose vitamin C through a vein to patients with hard-to-treat cancers such as ovarian, pancreatic or brain tumors.

From Science Daily ● Aug. 7, 2026

The tumors also appeared at lower levels of feeding — in fact, a level that produced no effect was not found.

From "Silent Spring" by Rachel Carson

Related Words

• Cancer
• carcinoma
• cyst
• lump
• swelling