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

Derived Forms

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

The samples were collected during tumor surgeries and came from both people with dementia and individuals without the condition.

From Science Daily • Jun. 8, 2026

J&J said the Firelink platform is a novel approach to overcome limitations of existing treatments by delivering a highly selective protein degrader to tumor cells, while avoiding healthy cells.

From The Wall Street Journal • Jun. 8, 2026

The approach involves collecting a patient's own immune cells, genetically modifying them to recognize cancer, and then returning them to the body to seek out and destroy tumor cells.

From Science Daily • Jun. 2, 2026

He based the upgrade on an “increasing conviction” in a rising class of cancer medication that simultaneously targets immune evasion and blood supply, two pathways crucial to tumor persistence.

From Barron's • May 27, 2026

“Your MRI came back clean. It means you don’t have a brain tumor, or anything like that.”

From "Challenger Deep" by Neal Shusterman

Related Words

• Cancer
• carcinoma
• cyst
• lump
• swelling