a synthetic hormone, CHNO, used as an estrogen-blocking drug to inhibit the growth of certain types of tumors, esp. in cases of advanced breast cancer: in full
See tamoxifen in American Heritage Dictionary 4
(tə-mŏkˈsə-fĕn)
noun
A nonsteroidal estrogen antagonist used in the treatment of advanced breast cancer in women whose tumors are estrogen-dependent and also used prophylactically by some women at risk for breast cancer.