estrogen Definition

any of various natural steroids (such as estradiol) that are formed from androgen precursors, that are secreted chiefly by the ovaries, placenta, adipose tissue, and testes, and that stimulate the development of female secondary sex characteristics and promote the growth and maintenance of the female reproductive system; also : any of various synthetic or semisynthetic steroids (such as ethinyl estradiol) that mimic the physiological effect of natural estrogens

hormone replacement therapy involving the administration of estrogen without progestin

any of a class of drugs (such as raloxifene or tamoxifen) that bind with estrogen receptors (as of the breast, uterus, or bone) and act as agonists to enhance estrogen activity in some tissues and as antagonists to inhibit estrogen activity in other tissues —called also SERM