Definitions

from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. A membranous vascular organ that develops in female mammals during pregnancy, lining the uterine wall and partially enveloping the fetus, to which it is attached by the umbilical cord. Following birth, the placenta is expelled.
  • n. An organ with similar functions in some nonmammalian animals, such as certain sharks and reptiles.
  • n. Botany The part within the ovary of a flowering plant to which the ovules are attached.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. A vascular organ in mammals, except monotremes and marsupials, present only in the female during gestation. It supplies food and oxygen from the mother to the foetus, and passes back waste. It is implanted in the wall of the uterus and links to the foetus through the umbilical cord. It is expelled after birth.
  • n. In flowering plants, the part of the ovary where ovules develop; in non-flowering plants where the spores develop.

from the GNU version of the Collaborative International Dictionary of English

  • n. The vascular appendage which connects the fetus with the parent, and is cast off in parturition with the afterbirth.
  • n. The part of a pistil or fruit to which the ovules or seeds are attached.

from The Century Dictionary and Cyclopedia

  • n. In zoöl., anat., and medicine: The organ of attachment of a vertebrate embryo or fetus to the wall of the uterus or womb of the female.
  • n. In echinoderms, a flat discoidal sea-urchin, as a sand-dollar or cake-urchin: used in a generic sense by Klein, 1734.
  • n. [capitalized] A genus of bivalve mollusks, now called Plaruna.
  • n. In botany, that part of the ovary of flowering plants which bears the ovules.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. the vascular structure in the uterus of most mammals providing oxygen and nutrients for and transferring wastes from the developing fetus
  • n. that part of the ovary of a flowering plant where the ovules form

Etymologies

New Latin, from Latin, flat cake, alteration of Greek plakoenta, from accusative of plakoeis, flat, from plax, plak-, flat land, surface; see plāk-1 in Indo-European roots.
(American Heritage® Dictionary of the English Language, Fourth Edition)
From Medieval Latin placenta uterina ("uterine cake"), from Latin placenta ("flat cake"), because of the flat round shape of the afterbirth. (Wiktionary)

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