cotyledon

noun

cot·​y·​le·​don ˌkä-tə-ˈlē-dᵊn 

plural cotyledons

1

: the first leaf or one of the first pair or whorl of leaves developed by the embryo of a seed plant see seedling illustration

2

: a small lobe of the mammalian placenta that facilitates the delivery of oxygen and nutrients to the fetus

cotyledonary

ˌkä-tə-ˈlē-də-ˌner-ē 

adjective

cotyledonary position

Examples of cotyledon in a Sentence

Recent Examples on the Web

When the sprouts produce their second pair of leaves (which are their true leaves; the first pair are called cotyledons), use sharp scissors to clip them at the soil line and enjoy them in smoothies, salads, sandwiches or stir-fries. — ABC News, 12 May 2026

When planting seed directly in the ground, water at least once a day until three sets of true leaves (not cotyledons or seed leaves) have developed. — Joshua Siskin, Oc Register, 18 Apr. 2026

These are leaf-like structures, called cotyledons, that are part of the seed and serve as food sources until true leaves are formed and the plant becomes capable of photosynthesis. — Kerry Michaels, The Spruce, 21 Jan. 2026

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 2

Kids Definition

cotyledon

noun

cot·​y·​le·​don ˌkät-ᵊl-ˈēd-ᵊn 

: the first leaf or one of the first leaves developed by the embryo of a seed plant that is usually folded within the seed until germination and serves as a storehouse of food

called also seed leaf

Medical Definition

cotyledon

noun

cot·​y·​le·​don ˌkät-ᵊl-ˈēd-ᵊn 

1

: a lobule (see lobule sense 2) of a mammalian placenta that facilitates the delivery of oxygen and nutrients to the fetus

2

: the first leaf or one of the first pair or whorl of leaves developed by the embryo of a seed plant

cotyledonary

-ˈēd-ᵊn-ˌer-ē 

adjective