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
Instead, doctors found a brain tumor.
—Rachel Hale, USA Today, 9 Apr. 2026
Pancreatic NETs are a rare type of tumor that forms in hormone-making cells of the pancreas and may be benign or cancerous, according to the National Cancer Institute.
—ABC News, 8 Apr. 2026
For some advanced cancers, sequencing the tumor genome should be one of the first steps patients and physicians take.
—Angus Chen, STAT, 7 Apr. 2026
Such mutations can accelerate a tumor’s growth, making the cancer harder and harder to treat and sometimes, as in this instance, claiming the patient’s life.
—Jerome Groopman, New Yorker, 6 Apr. 2026
See All Example Sentences for tumor
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Rachel Hale, USA Today, 9 Apr. 2026
Pancreatic NETs are a rare type of tumor that forms in hormone-making cells of the pancreas and may be benign or cancerous, according to the National Cancer Institute.
—ABC News, 8 Apr. 2026
For some advanced cancers, sequencing the tumor genome should be one of the first steps patients and physicians take.
—Angus Chen, STAT, 7 Apr. 2026
Such mutations can accelerate a tumor’s growth, making the cancer harder and harder to treat and sometimes, as in this instance, claiming the patient’s life.
—Jerome Groopman, New Yorker, 6 Apr. 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 12 Apr. 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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