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’s plausible but difficult to detect without screening people at a very young age, but there could also be difference in the progression of the tumors themselves, Cercek says.
—Lauren J. Young, Scientific American, 22 Jan. 2026
The orbital lab will support three-dimensional tumor growth experiments.
—Aamir Khollam, Interesting Engineering, 22 Jan. 2026
And Aaron Babier, a PhD candidate at the University of Toronto, developed AI software that reduces radiation therapy planning time from days to just 20 minutes after his stepmother died from a brain tumor.
—Craig S. Smith, Forbes.com, 21 Jan. 2026
Doctors revealed that Charlie had an aggressive tumor pushing against his lung, and he was sent to Leeds General Infirmary for life-saving treatment, per The Yorkshire Post.
—Escher Walcott, PEOPLE, 19 Jan. 2026
See All Example Sentences for tumor
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Lauren J. Young, Scientific American, 22 Jan. 2026
The orbital lab will support three-dimensional tumor growth experiments.
—Aamir Khollam, Interesting Engineering, 22 Jan. 2026
And Aaron Babier, a PhD candidate at the University of Toronto, developed AI software that reduces radiation therapy planning time from days to just 20 minutes after his stepmother died from a brain tumor.
—Craig S. Smith, Forbes.com, 21 Jan. 2026
Doctors revealed that Charlie had an aggressive tumor pushing against his lung, and he was sent to Leeds General Infirmary for life-saving treatment, per The Yorkshire Post.
—Escher Walcott, PEOPLE, 19 Jan. 2026
See All Example Sentences for tumor
Cite this Entry
“Tumor.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/tumor. Accessed 23 Jan. 2026.
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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