Thymosin is a hormone that helps to regulate the immune system. It is produced by the thymus gland and is involved in the development and maturation of T-cells. In some cases, thymosin can also stimulate the production of other hormones such as testosterone. There are several synonyms for the word thymosin, including thymic factor, thymic protein, and thymus factor. These terms essentially refer to the same hormone and are often used interchangeably in medical literature. Understanding the role of thymosin in the immune system is important for understanding how the body fights off disease and infection.