Tamoxifen

n.
  1. a chemical compound (C26H29NO) which is non-steroidal but physiogically active as an estrogen antagonist. It is used to treat postmenopausal breast cancer. Chemically it is 1-p-dimethylaminoethoxyphenyl-trans-1,2-diphenyl-but-1-ene. It can be obtained as a white crystalline powder.