a. The portion of the egg of egg-laying vertebrates, such as reptiles and birds, and of certain invertebrates that consists chiefly of protein and fat and serves as the primary source of nourishment for the early embryo.
b. This portion of the egg of a bird, especially a chicken, which is large, yellow, and surrounded by albumen.
2. A greasy substance found in unprocessed sheep's wool, which is refined to make lanolin.
[Middle English yolke, from Old English geolca, from geolu, yellow; see YELLOW.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.