yolk

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.

noun

1. the substance in an animal ovum consisting of protein and fat that nourishes the developing embryoRelated adjective: vitelline
2. a greasy substance secreted by the skin of a sheep and present in the fleece

Old English geolca, geoloca “yolk,” literally “the yellow part,” from geolu “yellow” (see yellow). Formerly also spelled yelk. n.

1. The portion of the egg of an animal that consists of protein and fat from which the early embryo gets its main nourishment and of protoplasmic substances from which the embryo develops.

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.