A yolk is the inner, yellow part of an egg. If you order eggs "sunny side up," those "suns" are the egg yolks.

When a bird lays an egg that's fertilized and begins to grow into a baby bird, the yolk is the substance that nourishes the bird embryo. The eggs we eat have yolks too, but since they are unfertilized, these protein-rich yolks can be beaten into omelettes or mixed into cake batter. The Old English root of yolk, geolca, literally means "the yellow part."

Definitions of yolk
  1. noun
    nutritive material of an ovum stored for the nutrition of an embryo (especially the yellow mass of a bird or reptile egg)
    synonyms: vitellus
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    type of:
    food, nutrient
    any substance that can be metabolized by an animal to give energy and build tissue
  2. noun
    the yellow spherical part of an egg that is surrounded by the albumen
    synonyms: egg yolk
    see moresee less
    type of:
    fixings, ingredient
    food that is a component of a mixture in cooking
Word Family

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