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
After surgery to remove the tumor, a biopsy revealed that Ni had stage III-C high-grade serous ovarian cancer, an advanced stage of ovarian cancer.
—Ciara McCarthy 9, Fort Worth Star-Telegram, 9 Sep. 2025
He was eventually diagnosed with a brain tumor.
—David Chiu, PEOPLE, 8 Sep. 2025
The Gilberts’ son Nick, one of their five children, died in May 2023 from neurofibromatosis, a rare genetic disease that causes non-cancerous tumors to grow on nerves throughout the body, likely putting an unimaginable strain on the family.
—Giacomo Tognini, Forbes.com, 8 Sep. 2025
Novartis’s radioligand therapy targets mutations in tumors, delivering radiation only where it is needed, unlike ordinary radiotherapy which kills non-cancerous cells as well as cancerous ones.
—Ben Smith, semafor.com, 8 Sep. 2025
See All Example Sentences for tumor
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Ciara McCarthy 9, Fort Worth Star-Telegram, 9 Sep. 2025
He was eventually diagnosed with a brain tumor.
—David Chiu, PEOPLE, 8 Sep. 2025
The Gilberts’ son Nick, one of their five children, died in May 2023 from neurofibromatosis, a rare genetic disease that causes non-cancerous tumors to grow on nerves throughout the body, likely putting an unimaginable strain on the family.
—Giacomo Tognini, Forbes.com, 8 Sep. 2025
Novartis’s radioligand therapy targets mutations in tumors, delivering radiation only where it is needed, unlike ordinary radiotherapy which kills non-cancerous cells as well as cancerous ones.
—Ben Smith, semafor.com, 8 Sep. 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 10 Sep. 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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