1. (noun)menstruation, menses, menstruum, catamenia, period, flow the monthly discharge of blood from the uterus of nonpregnant women from puberty to menopause Synonyms: menstruum, flow rate, current, flowing, menses, menstruation, period of time, full point, stream, full stop, catamenia, time period, stop, period, flow, point, geological period, rate of flow