Tamoxifen \Ta*mox"i*fen\ (t[a^]*m[o^]k"s[i^]*f[e^]n), n. 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. --[MI11] Syn: Kessar; Noltam; Nolvadex; Tamofen; Tamoxasta; Terimon; Xynoplex. [PJC]