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1. The yellow part of an egg; the vitellus.

2. (Science: zoology) An oily secretion which naturally covers the wool of sheep.

(Science: anatomy) Yolk cord, the umbilical vesicle. See Unbilical.

Origin: OE. Yolke, yelke, yolke, yelke, AS. Geoloca, geoleca, fr. Geolu yellow. See Yellow

Alternative forms: yelk. Nutritive material of an ovum stored for the nutrition of an embryo (especially the yellow mass of a bird or reptile egg).The part of eggs that contains nutrients, primarily consisting of protein and fat molecules which provide the basic building blocks of life. Evolutionary change has resulted in changes in mammal eggs, where the embryo obtains food from the placenta as opp.