Primary amenorrhea: Absence of menstruation. Amenorrhea is conventionally divided into primary and secondary amenorrhea. With primary amenorrhea, menstruation never takes place. It fails to occur at puberty. With secondary amenorrhea, menstruation starts but then stops. The absence of menstruation during pregnancy is a form of physiologic amenorrhea, physiologic in the sense that it is completely normal and is not caused by anything pathologic. Amenorrhea during lactation is another type of physiologic amenorrhea. The word "amenorrhea" is compounded from three Greek roots "a-", no + "men", month + "rhoia", flow = no monthly flow. Amenorrhea is less commonly called amenia.