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
It can be caused by adrenal tumors, long-term steroid use, or conditions affecting the pituitary gland (a gland in your brain that controls hormone production).
—Brandi Jones, Health, 6 June 2025
This functional imaging approach can reveal cancers that are otherwise hidden in dense breast tissue, which appears white on mammograms—the same color as many tumors.
—Lauryn Higgins, Flow Space, 6 June 2025
Ten of these children have been diagnosed with cancer, including leukemia, brain tumors and lymphomas.
—William A. Haseltine, Forbes.com, 4 June 2025
Afterward, the plastic surgeon told Miranda and Bryan that Cameron, now 4, had done great and described the mass as fatty tissue, not a typical cyst or tumor.
—Jordan Greene, People.com, 2 June 2025
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Brandi Jones, Health, 6 June 2025
This functional imaging approach can reveal cancers that are otherwise hidden in dense breast tissue, which appears white on mammograms—the same color as many tumors.
—Lauryn Higgins, Flow Space, 6 June 2025
Ten of these children have been diagnosed with cancer, including leukemia, brain tumors and lymphomas.
—William A. Haseltine, Forbes.com, 4 June 2025
Afterward, the plastic surgeon told Miranda and Bryan that Cameron, now 4, had done great and described the mass as fatty tissue, not a typical cyst or tumor.
—Jordan Greene, People.com, 2 June 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 17 Jun. 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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