tamoxifen UK /təˈmɒk.sɪ.fɛn/US /təˈmɑk.sɪf.ən/ noun1 •A nonsteroidal estrogen antagonist used in the treatment of postmenopausal breast cancer and infertility in women.Treatment with tamoxifen after surgery reduced cancer relapse rates by nearly 50 percent. — 2010 formstamoxifens
