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
Here, the researchers transplanted three types of human tumor – lung, prostate and colon – into mouse models of AD.
—New Atlas, 29 Jan. 2026
Keeping him in power is like performing surgery and knowingly leaving a cancerous tumor behind.
—Gustavo Arellano, Los Angeles Times, 29 Jan. 2026
In 2002, doctors discovered and removed a tumor on his spinal cord.
—Richard Ruelas, AZCentral.com, 29 Jan. 2026
By that time, the team had realized that KL-50 might have potential beyond treating brain tumors.
—Isabella Backman, Hartford Courant, 27 Jan. 2026
See All Example Sentences for tumor
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New Atlas, 29 Jan. 2026
Keeping him in power is like performing surgery and knowingly leaving a cancerous tumor behind.
—Gustavo Arellano, Los Angeles Times, 29 Jan. 2026
In 2002, doctors discovered and removed a tumor on his spinal cord.
—Richard Ruelas, AZCentral.com, 29 Jan. 2026
By that time, the team had realized that KL-50 might have potential beyond treating brain tumors.
—Isabella Backman, Hartford Courant, 27 Jan. 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 1 Feb. 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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