də̇ˈsijəwə, dēˈ- noun
( plural decid·uae -ˌwē)
Etymology: New Latin, from Latin, feminine of deciduus deciduous
1. : the part of the mucous membrane lining the uterus that in higher placental mammals undergoes special modifications in preparation for and during pregnancy and is cast off at parturition, being made up in the human of (1) a part lining the uterus, (2) a part enveloping the embryo, and (3) a part participating with the chorion in the formation of the placenta — called also respectively (1) decidua ve.ra -ˈvirə, (2) decidua cap.su.lar.is -ˌkapsəˈla(a)rə̇s or decidua re.flexa -rə̇ˈfleksə, and (3) decidua ser.o.ti.na -ˌserəˈtīnə, -tē-
2. : the part of the mucous membrane of the uterus cast off in the ordinary process of menstruation — called also decidua men·stru·al·is -ˌmenztrəˈwalə̇s