'Yolk' definitions:

Definition of 'yolk'

noun

The yellow spherical part of an egg that is surrounded by the albumen [syn: egg yolk, yolk]

noun

Nutritive material of an ovum stored for the nutrition of an embryo (especially the yellow mass of a bird or reptile egg) [syn: yolk, vitellus]

From: GCIDE

Yolk \Yolk\ (y[=o]lk or y[=o]k; 277), n. [OE. yolke, yelke, [yogh]olke, [yogh]elke, AS. geoloca, geoleca, fr. geolu yellow. See Yellow.] [Written also yelk.] [1913 Webster]
1. The yellow part of an egg; the vitellus. [1913 Webster]
2. (Zool.) An oily secretion which naturally covers the wool of sheep. [1913 Webster]
Yolk cord (Zool.), a slender cord or duct which connects the yolk glands with the egg chambers in certain insects, as in the aphids.
Yolk gland (Zool.), 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 (Anat.), the umbilical vesicle. See under Unbilical. [1913 Webster]