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
However, despite the aggressive treatment, an MRI in September 2025 revealed that Cara’s tumor had returned and spread to her spine.
—Toria Sheffield, PEOPLE, 6 June 2026
Rather than attacking all rapidly growing cells, as chemotherapy does, the drug targets a key cancer-driving pathway known as KRAS, which is involved in more than 90% of pancreatic tumors.
—Luzdelia Caballero, CBS News, 5 June 2026
In the year following his diagnosis, Spier had multiple surgeries to remove cancerous tumors from his brain.
—Brad Quick, CNBC, 5 June 2026
The drug doubled survival time and kept tumors from growing for twice as long compared to conventional chemotherapy.
—Lisa Jarvis, Mercury News, 4 June 2026
See All Example Sentences for tumor
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Toria Sheffield, PEOPLE, 6 June 2026
Rather than attacking all rapidly growing cells, as chemotherapy does, the drug targets a key cancer-driving pathway known as KRAS, which is involved in more than 90% of pancreatic tumors.
—Luzdelia Caballero, CBS News, 5 June 2026
In the year following his diagnosis, Spier had multiple surgeries to remove cancerous tumors from his brain.
—Brad Quick, CNBC, 5 June 2026
The drug doubled survival time and kept tumors from growing for twice as long compared to conventional chemotherapy.
—Lisa Jarvis, Mercury News, 4 June 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 9 Jun. 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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