yolk

American  

[yohk, yohlk] / yoʊk, yoʊlk /

noun

1. the yellow and principal substance of an egg, as distinguished from the white.

2. Embryology. the part of the contents of the egg of an animal that enters directly into the formation of the embryo, together with any material that nourishes the embryo during its formation.

3. the essential part; the inner core.

4. a natural grease exuded from the skin of sheep.

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yolk British  

/ jəʊk /

noun

1. the substance in an animal ovum consisting of protein and fat that nourishes the developing embryo

2. a greasy substance secreted by the skin of a sheep and present in the fleece

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yolk Scientific  

/ yōk /

1. The yellow internal part of the egg of a bird or reptile. The yolk is surrounded by the albumen and supplies food to the developing young.

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Other Word Forms

• yolked adjective
• yolkless adjective
• yolky adjective

Etymology

Origin of yolk

before 1000; Middle English yolke, yelke, Old English geoloca, derivative of geolu yellow

Example Sentences

"When they are small, they kind of look like an elephant squished into a little yolk sack."

From Science Daily • Oct. 16, 2025

Battling strong currents, Ralph Pace captured this image of a swell shark egg case, revealing a glowing embryo, complete with gill slits and a yolk sac.

From BBC • Oct. 14, 2025

Eventually, membrane or no, there will be some gas exchange, causing the egg white to become more watery and leak into the yolk, ultimately breaking the yolk.

From Slate • Apr. 19, 2025

The richness of the egg yolk and oil provides the fat, while vinegar or lemon adds the acidity and just a touch of salt rounds everything out.

From Salon • Mar. 27, 2025

I cracked an egg and cupped out the yolk and dropped white and shells into the pot, for I know nothing that polishes coffee and makes it shine like that.

From "Travels with Charley in Search of America" by John Steinbeck