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
That study has enrolled only nine patients, however, and the results so far show that just one patient’s tumor actually shrank, according to a recent scientific abstract.
—Benjamin Mazer, The Atlantic, 17 June 2025
The study examined patients with advanced triple-negative breast cancer whose tumors express PD-L1.
—Annika Kim Constantino, CNBC, 17 June 2025
Most commonly, tumors occur in the retina, brain, spinal chord and kidneys.
—Alice Gibbs, MSNBC Newsweek, 17 June 2025
One undergoes regular screening; her tumor is caught early.
—Siddhartha Mukherjee, New Yorker, 16 June 2025
See All Example Sentences for tumor
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Benjamin Mazer, The Atlantic, 17 June 2025
The study examined patients with advanced triple-negative breast cancer whose tumors express PD-L1.
—Annika Kim Constantino, CNBC, 17 June 2025
Most commonly, tumors occur in the retina, brain, spinal chord and kidneys.
—Alice Gibbs, MSNBC Newsweek, 17 June 2025
One undergoes regular screening; her tumor is caught early.
—Siddhartha Mukherjee, New Yorker, 16 June 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 28 Jun. 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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