Yolk /(yōlk [or] yōk; 277)/

Yolk

n.
  1. The yellow part of an egg; the vitellus.
  2. An oily secretion which naturally covers the wool of sheep. (Zool.)

Phrases & Compounds
Yolk cord
a slender cord or duct which connects the yolk glands with the egg chambers in certain insects, as in the aphids.
Yolk gland
a special organ which secretes the yolk of the eggs in many turbellarians, and in some other invertebrates. See Illust. of Hermaphrodite in Appendix.
Yolk sack
the umbilical vesicle. See under Unbilical.