'Placenta' definitions:

Definition of 'placenta'

noun

That part of the ovary of a flowering plant where the ovules form

noun

The vascular structure in the uterus of most mammals providing oxygen and nutrients for and transferring wastes from the developing fetus

From: GCIDE

Placenta \Pla*cen"ta\, n.; pl. L. Placent[ae], E. Placentas. [L., a cake, Gr. ? a flat cake, from ? flat, fr. ?, ?, anything flat and broad.]
1. (Anat.) The vascular appendage which connects the fetus with the parent, and is cast off in parturition with the afterbirth. [1913 Webster]
Note: In most mammals the placenta is principally developed from the allantois and chorion, and tufts of vascular villi on its surface penetrate the blood vessels of the parental uterus, and thus establish a nutritive and excretory connection between the blood of the fetus and that of the parent, though the blood itself does not flow from one to the other. [1913 Webster]
2. (Bot.) The part of a pistil or fruit to which the ovules or seeds are attached. [1913 Webster]