thymus

noun

thy·​mus ˈthī-məs 

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

To prevent damage, our body tries to eliminate malfunctioning T cells in a lymphoid organ in the chest, called the thymus, through a process known as central tolerance, according to The Associated Press. —Freddie Clayton, NBC news, 6 Oct. 2025

Alongside colleagues in Japan in the 1980s and 1990s, Sakaguchi wanted to figure out why, when batches of immune cells from healthy mice were injected into mice that had their thymuses removed, the cells didn't trigger an autoimmune disease. —Beth Mole, ArsTechnica, 6 Oct. 2025

For decades, scientists thought self-tolerance was primarily established in the parts of the body that make immune cells, such as the thymus for T cells and the bone marrow for B cells. —Aimee Pugh Bernard, The Conversation, 6 Oct. 2025

And the thymus gland, the producer of white blood cells, shrinks and weakens over time. —Jocelyn Solis-Moreira, Flow Space, 30 Sep. 2025

Word History

Etymology

New Latin, from Greek thymos warty excrescence, thymus

First Known Use

1578, in the meaning defined above

Rhymes for thymus

• imus
• primus

Kids 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