[n] the mucous membrane that lines the uterus; thickens under hormonal control and (if pregnancy does not occur) is shed in menstruation; if pregnancy occurs it is shed along with the placenta at parturition
\En`do*me"tri*um\, n. [NL., fr. Gr. 'e`ndon within + mh`tra the womb.] (Anat.) The membrane lining the inner surface of the uterus, or womb.