(1) /es·trone/ (es´tron) an estrogen isolated from pregnancy urine, human placenta, palm kernel oil, and other sources, also prepared synthetically;
(2) <chemical> 3-hydroxyestra-1,3,5(10)-trien-17-one. A metabolite of estradiol but possessing less biological activity. It is found in the urine of pregnant women and mares, in the human placenta, and in the urine of bulls and stallions. According to the fourth annual report on carcinogens (ntp 85-002, 1985), estrone may reasonably be anticipated to be a carcinogen (merck, 11th ed).