tumor

American  

[too-mer, tyoo-] / ˈtu mər, ˈtyu- /

especially British, tumour

noun

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

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

Etymology

Origin of tumor

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

Their work centers on understanding how cancer cells interact with their surroundings, often referred to as the tumor microenvironment.

From Science Daily • Apr. 12, 2026

In this case, the virus has been modified to replicate only inside tumor cells, causing them to burst, while simultaneously triggering a more aggressive immune response from the body’s own white blood cells.

From Barron's • Apr. 10, 2026

The Foster City, Calif., company said the deal also includes TUB-030, an ADC that has shown promising initial clinical data across various solid tumor types.

From The Wall Street Journal • Apr. 7, 2026

The study also showed that KLF5 regulates other genes, including NCAPD2 and MTHFD1, but only in metastatic pancreatic cancer cells, not in primary tumor cells grown in the lab.

From Science Daily • Apr. 7, 2026

“Your cancer is not going away, Hazel. But we’ve seen people live with your level of tumor penetration for a long time.”

From "The Fault in Our Stars" by John Green

Related Words

• Cancer
• carcinoma
• cyst
• lump
• swelling