DES; the acronym for diethylstilbestrol, a synthetic, nonsteroidal form of estrogen. A well-known teratogen and carcinogen, DES inhibits the hypothalamic-pituitary-gonadal axis, thereby blocking the testicular synthesis of testosterone, lowering plasma testosterone, and inducing a chemical castration. OR A synthetic form of the hormone estrogen that was prescribed to pregnant women between about 1940 and 1971 because it was thought to prevent miscarriages. Diethylstilbestrol may increase the risk of uterine, ovarian, or breast cancer in women who took it. It also has been linked to an increased risk of clear cell carcinoma of the vagina or cervix in daughters exposed to diethylstilbestrol before birth. Also called DES.