antiestrogen an·ti·es·tro·gen (ān'tē-ěs'trə-jən, ān'tī-)
A substance capable of preventing full expression of the biological effects of an estrogen.
estrogen es·tro·gen or oes·tro·gen (ěs'trə-jən)
Any of several natural or synthetic substances formed by the ovary, placenta, testis, and certain plants, that stimulate the female secondary sex characteristics, exert systemic effects such as the growth and maturation of long bones, and are used to treat disorders due to estrogen deficiency and to ameliorate cancers of the breast and prostate. Also called estrin.