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
Just 1% of the national spend on cancer research is allocated to brain tumors.
—Escher Walcott, PEOPLE, 30 Sep. 2025
While these tumors are not cancerous, both women have suffered long-term side effects.
—Lucy Notarantonio, MSNBC Newsweek, 28 Sep. 2025
In those cases, if someone goes into remission, disseminated cancer cells (DCCs)—which have broken away from a primary tumor and spread to distant organs—can remain dormant in the body for years or even decades before metastatic relapse.
—Elizabeth Yuko, Flow Space, 24 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
See All Example Sentences for tumor
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Escher Walcott, PEOPLE, 30 Sep. 2025
While these tumors are not cancerous, both women have suffered long-term side effects.
—Lucy Notarantonio, MSNBC Newsweek, 28 Sep. 2025
In those cases, if someone goes into remission, disseminated cancer cells (DCCs)—which have broken away from a primary tumor and spread to distant organs—can remain dormant in the body for years or even decades before metastatic relapse.
—Elizabeth Yuko, Flow Space, 24 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
See All Example Sentences for tumor
Cite this Entry
“Tumor.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/tumor. Accessed 3 Oct. 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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