1
: an abnormal benign or malignant new growth of tissue that possesses no physiological function and arises from uncontrolled usually rapid cellular proliferation
called also neoplasm
2
: a swollen or distended part
… houses that bulged with the tumors and warts of … ornamental architecture …—
W. A. White
W. A. WhiteExamples of tumor in a Sentence
the scan showed a small tumor in her abdomen
Recent Examples on the Web
Older women may also be more likely to develop estrogen receptor-positive tumors, Giordano notes.
—Korin Miller, Flow Space, 7 Oct. 2025
Further investigation of human brain scans found that skull thickness had been altered by the tumors, particularly where bones fuse.
—New Atlas, 6 Oct. 2025
For cancer, the goal is to inhibit Tregs, allowing the immune system to target tumors more aggressively.
—Aimee Pugh Bernard, The Conversation, 6 Oct. 2025
The tumor made eating painful and left her only days to weeks to live.
—Alice Gibbs, MSNBC Newsweek, 3 Oct. 2025
See All Example Sentences for tumor
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Korin Miller, Flow Space, 7 Oct. 2025
Further investigation of human brain scans found that skull thickness had been altered by the tumors, particularly where bones fuse.
—New Atlas, 6 Oct. 2025
For cancer, the goal is to inhibit Tregs, allowing the immune system to target tumors more aggressively.
—Aimee Pugh Bernard, The Conversation, 6 Oct. 2025
The tumor made eating painful and left her only days to weeks to live.
—Alice Gibbs, MSNBC Newsweek, 3 Oct. 2025
See All Example Sentences for tumor
Cite this Entry
“Tumor.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/tumor. Accessed 8 Oct. 2025.
Copy CitationKids Definition
tumor
noun
tu·mor
ˈt(y)ü-mər 
: an abnormal mass of tissue that arises from normal tissue cells and serves no useful purpose in the body
tumorous
adjective
ˈt(y)üm-(ə-)rəs
Medical Definition
tumor
noun
tu·mor
variants
or chiefly British tumour
: an abnormal benign or malignant new growth of tissue that possesses no physiological function and arises from uncontrolled usually rapid cellular proliferation see cancer sense 1, carcinoma, sarcoma
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