[de.cid.ua] n, pl -u.ae [NL, fr. L, fem. of deciduus] (1785) 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
2: the part of the mucous membrane of the uterus cast off in the process of menstruation -- de.cid.u.al adj