- menstrual cycle - a recurring cycle (beginning at menarche and ending at menopause) in which the endometrial lining of the uterus prepares for pregnancy; if pregnancy does not occur the lining is shed at menstruation; "the average menstrual cycle is 28 days"
--1 is a kind of cycle, oscillation
--1 has parts:fertile period, fertile phase; menstrual phase; secretory phase, luteal phase; safe period