cotyledon
noun
cot·y·le·don ˌkä-tə-ˈlē-dᵊn 
1
: a lobule of the mammalian placenta
2
: 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 (such as ferns) see seedling illustration
cotyledonary
ˌkä-tə-ˈlē-də-ˌner-ē
adjective 
Word History
Etymology
New Latin, from Greek kotylēdōn cup-shaped hollow, from kotylē cup, anything hollow
First Known Use
1540, in the meaning defined at sense 1
Kids Definition
cotyledon
noun
cot·y·le·don ˌkä-tə-ˈlē-dᵊn
: the first leaf or one of the first leaves of a plant which is usually folded within a seed until germination and which serves as a storehouse of food for the plant
Medical Definition
cotyledon
noun
cot·y·le·don ˌkät-ᵊl-ˈēd-ᵊn
1
: a lobule of a mammalian placenta
2
: 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)