cot·y·le·don noun \ˌkät-əl-ˈēd-ən\
: a lobule of a mammalian placenta
: the first leaf or one of the first pair or whorl of leaves developed by the embryo of a seed plant or of some lower plants (as ferns)
—cot·y·le·don·ary \-ˈēd-ən-ˌer-ē\ adjective
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