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

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 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

Gilead and Tubulis inked an exclusive option and license agreement in 2024 aimed at discovering and developing an ADC against a solid tumor target.

From The Wall Street Journal • Apr. 7, 2026

Removal of the tumor was scheduled for two months later, so Duong went home to his family for the weekend.

From Los Angeles Times • Mar. 30, 2026

Doctors had done a small operation just after I was born to remove the tumor that split the middle of my face and caused my facial deformities.

From "Ugly" by Robert Hoge

Related Words

• Cancer
• carcinoma
• cyst
• lump
• swelling