Dictionary.net

• The supposed disintegration and removal, during menstruation, of certain epithelial elements, potentially the nidus of an embryo.

1898 - American pocket medical dictionary
By Willam Alexander Newman Dorland

• The process by which the superficial portion of the mucous membrane of the body of the uterus, after having become tumid and succulent during menstruation, is said to be disintegrated and cast off. [Lat.]

1916 - Appleton's medical dictionary
By Smith Ely Jelliffe