Merriam-Webster Collegiate Dictionary - estrogen

 noun  Etymology: New Latin estrus + International Scientific Vocabulary -o- + -gen  Date: 1927 any of various natural steroids (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 (as ethinyl estradiol) that mimic the physiological effect of natural ~s