progesterone: a hormone produced by the ovaries after ovulation and in lesser amounts by the adrenal glands. A precursor to most of the steroid hormones, it has many vital functions, from maintaining pregnancy to regulating menstrual cycles. It has calming and diuretic properties, and enhances the beneficial effects of estrogens while balancing estrogen and preventing problems linked to estrogen excess. Progesterone also facilitates balance of other steroid hormones.