\Cot`y*le"don\ (k?t`?-l?"d?n), n. [Gr.??? a cupshaped
hollow, fr. ???. See {Cotyle}.]
1. (Anat.) One of the patches of villi found in some forms of
   placenta.

2. (Bot.) A leaf borne by the caulicle or radicle of an
   embryo; a seed leaf.

Note: Many plants, as the bean and the maple, have two
      cotyledons, the grasses only one, and pines have
      several. In one African plant ({Welwitschia}) the
      cotyledons are permanent and grow to immense
      proportions.