Definition of "yolk" []

• The yellow, usually spherical portion of an egg of a bird or reptile, surrounded by the albumen and serving as nutriment for the developing young. (noun)
• A corresponding portion of the egg of other animals, consisting of protein and fat that serve as the primary source of nourishment for the early embryo and protoplasmic substances from which the embryo develops. (noun)
• A greasy substance found in unprocessed sheep's wool. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Boil it — hard-boil it — until the yolk is a firm yellow globe — a sun shining on manly hearts with cleaned-out ears."
• "Soft-boiled inside the shell, they furnish a self-contained hot meal (best at just about five minutes, so that the yolk is still runny but the white more or less set)."
• "Make sure to scrape the sides of the bowl after each egg yolk is added."