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

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

Vegetables: Unlike sprouts that are consumed just 3-7 days after seeds are planted, microgreens, as the name implies, are harvested for their green cotyledons (or first leaves) and stems between 1-3 weeks after their seeds are sown. —Joshua Siskin, Oc Register, 17 July 2025

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