from 1540s, in various sense, from Latin cotyledon "pennywort, navelwort," from Greek kotyledon "cup-shaped cavity," from kotyle "hollow thing, small vessel," also the name of a small liquid measure (nearly a half-pint); of uncertain origin. Botanical sense is 1776, from Linnaeus (1751).
cotyledon cot·y·le·don (kŏt'l-ēd'n)
One of the lobules constituting the uterine side of the placenta, consisting mainly of a rounded mass of villi.
A leaf of the embryo of a seed plant, which, upon germination either remains in the seed or emerges, enlarges, and becomes green; a seed leaf.
A leaf of the embryo of a seed-bearing plant. Most cotyledons emerge, enlarge, and become green after the seed has germinated. Cotyledons either store food for the growing embryo (as in monocotyledons) or absorb food that has been stored in the endosperm (as in other angiosperms) for eventual distribution to the growing parts of the embryo. Also called seed leaf. See more at eudicotyledon, monocotyledon.