Definition of "thymus" [thymus ]

• A small glandular organ that is situated behind the top of the breastbone, consisting mainly of lymphatic tissue and serving as the site of T cell differentiation. The thymus increases gradually in size and activity until puberty, becoming vestigial thereafter. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "There are several things that can cause the thymus to atrophy, or decrease in size, which in turn leads to an insufficient number of these regulatory T cells being educated to keep an eye on other T cells."
• "Millions of T cells are “educated” in your thymus to perform specific roles—such as, say, to recognize and eradicate an infiltrating influenza-A germ or food-borne bacteria like salmonella from your body, as well as hundreds of other antigens with which your body may come into contact."
• "It is in the thymus that T cells mature before they enter your bloodstream."