a gland in the upper thorax or neck of all vertebrates, involved in the production of lymphocytes: in humans, it is most prominent at puberty, after which it disappears or becomes vestigial
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.