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The Collaborative International Dictionary of English v.0.48 (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.
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2. (Zool.) An oily secretion which naturally covers the wool
of sheep.
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{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]