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
Hamilton was diagnosed in 2024 with a brain tumor on the left side of her brain, which has also damaged the optic nerve in her left eye.
—Daniella Gray, MSNBC Newsweek, 24 Sep. 2025
Isabella received her diagnosis in October 2023 and underwent emergency surgery to remove a large medulloblastoma — a type of malignant tumor — in her cerebellum.
—Vanessa Etienne, PEOPLE, 22 Sep. 2025
Immunotherapy drugs like Keytruda stop the checkpoints from hiding cancer cells, allowing the immune system to locate and attack tumors.
—Tom Gavin, EverydayHealth.com, 22 Sep. 2025
Popokh decided to become a doctor after a twelve-year-old cousin died of a brain tumor.
—Dhruv Khullar, New Yorker, 22 Sep. 2025
See All Example Sentences for tumor
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Daniella Gray, MSNBC Newsweek, 24 Sep. 2025
Isabella received her diagnosis in October 2023 and underwent emergency surgery to remove a large medulloblastoma — a type of malignant tumor — in her cerebellum.
—Vanessa Etienne, PEOPLE, 22 Sep. 2025
Immunotherapy drugs like Keytruda stop the checkpoints from hiding cancer cells, allowing the immune system to locate and attack tumors.
—Tom Gavin, EverydayHealth.com, 22 Sep. 2025
Popokh decided to become a doctor after a twelve-year-old cousin died of a brain tumor.
—Dhruv Khullar, New Yorker, 22 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 28 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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