Webster's English Dictionary

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placenta

pla.cen.ta \pl*-'sent-*\ \-'sent-*l\ n [NL, fr. L, flat cake, fr. Gk 
   plakount-, plakous, fr. plak-,]plax flat surface - more at PLEASE 1a: the 
   vascular organ in mammals except monotremes and marsupials that uni tes 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 1b: an analogous organ in another animal  2: a 
   sporangium-bearing surface; esp : the part of the carpel beari ng ovules - 
   pla.cen.tal ajor ;n