Pronunciation: (yōk, yōlk),[key] —n. 1. the yellow and principal substance of an egg, as distinguished from the white.
2. Embryol.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. Also,yoke.