variants
or thymus gland
plural thymuses also thymi
ˈthī-ˌmī 
: a glandular structure of largely lymphoid tissue that functions especially in cell-mediated immunity by being the site where T cells develop, is present in the young of most vertebrates typically in the upper anterior chest or at the base of the neck, and gradually decreases in size and activity after puberty
Examples of thymus in a Sentence
Recent Examples on the Web
Megan Sykes, director of the Columbia Center for Translational Immunology in New York City, is tackling this by transplanting additional tissue from the donor’s immune system—either bone marrow cells or the thymus—into the recipient.
—
Amber Dance, Smithsonian Magazine, 7 Mar. 2025
The knife damaged soft tissue, muscles, the upper and lower lobes of his right lungs, the right lobe of his liver, his diaphragm, the ribs, the thymus gland and the heart itself, Arangelovich said.
—Michelle Mullins, Chicago Tribune, 28 Feb. 2025
In 1989, Hale was diagnosed with cancer of the thymus.
—Colson Thayer, People.com, 20 Jan. 2025
The addition of the thymus, a small organ in the upper chest that’s part of the immune system, was meant to help prevent rejection.
—Emily Mullin, WIRED, 17 Dec. 2024
See All Example Sentences for thymus
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Amber Dance, Smithsonian Magazine, 7 Mar. 2025
The knife damaged soft tissue, muscles, the upper and lower lobes of his right lungs, the right lobe of his liver, his diaphragm, the ribs, the thymus gland and the heart itself, Arangelovich said.
—Michelle Mullins, Chicago Tribune, 28 Feb. 2025
In 1989, Hale was diagnosed with cancer of the thymus.
—Colson Thayer, People.com, 20 Jan. 2025
The addition of the thymus, a small organ in the upper chest that’s part of the immune system, was meant to help prevent rejection.
—Emily Mullin, WIRED, 17 Dec. 2024
See All Example Sentences for thymus
Cite this Entry
“Thymus.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/thymus. Accessed 25 Jul. 2025.
Copy CitationKids Definition
thymus
noun
thy·mus
ˈthī-məs
plural thymuses also thymi
-ˌmī
: a gland that is found in the young of most vertebrates usually in the chest near the heart, that before and for a time after birth has very important effects on the production and development of T cells, and that becomes less active and gradually shrinks or disappears with age
Medical Definition
thymus
noun
thy·mus
ˈthī-məs
variants
or thymus gland
plural thymuses also thymi
-ˌmī
: a glandular structure of largely lymphoid tissue that functions in cell-mediated immunity by being the site where T cells develop, that is present in the young of most vertebrates typically in the upper anterior chest or at the base of the neck, that arises from the epithelium of one or more embryonic branchial clefts, and that gradually decreases in size and activity after puberty
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