[pla.cen.ta] n, pl -centas or -cen.tae [NL, fr. L, flat cake, fr. Gk plakoenta, acc. of plakoeis, fr. plak-, plax flat surface--more at fluke] (1691) 1: the vascular organ in mammals except monotremes and marsupials that unites the fetus to the maternal uterus and mediates its metabolic exchanges through a more or less intimate association of uterine mucosal with chorionic and usu. allantoic tissues; also: an analogous organ in another animal
2: a sporangium-bearing surface; esp: the part of the carpel bearing ovules -- pla.cen.tal adj or n